Such "standardization", while still very popular in many organizations, brings more harm than good. It's originates from a few myths:
Myth #1: All BI tools are basically the sameThis is no more true than saying "All airplanes are basically the same". Such altitude is coming from poor understanding of the purpose of Business Intelligence tools and capabilities of products available on the market. If two applications show charts and allow analyzing data it doesn't make them functionally equivalent because there is huge variety in the ways how data can be viewed and analyzed. Tell a good chef that all knives are basically the same therefore s/he should pick and use only one knife. Because, you know, "standardization".
BI tools are not the same. The task of data analysis and visualization is so complex and broad that no vendor can create a universal comprehensive solution, just like neither Boeing nor Airbus can create one universal airplane suitable for all cases -- from long passenger flights to air warfare to rescue operations.
For instance Qlik has amazing associative engine that allows easy discovery of logical relationships in data. Tableau has absolutely wonderful data visualization concept that unveils hidden patterns and provides meaningful perspectives that could be easily overlooked. Spotfire offers comprehensive means for scientific analysis and predictive modelling. The core concepts of these applications don't overlap. Some features surely do, but that doesn't make them interchangeable. Other BI tools also have their strong features. Any analytical application that has deeply thought-out, fundamental concept behind it will be significantly different from others.
Myth #2: Standardization is always a good thingThis myth is logically connected to Myth #1. Standardization, when it's applicable, has obvious benefits most of which boil down to one -- cost reduction. A company can get a deeper discount if it purchases more software licenses. You can save on training if you train employees only for 1 tool, instead of many. More people with similar skills are interchangeable, therefore less risk of losing critical expertise, also reduced staff count. And so on.
However, any cost reduction is only good when it doesn't degrade key functional capabilities. What would happen if you force a chef to "standardize" on knives? His/her functional capability would degrade. What would happen if you tell a military air force to use the same type of plane for cargo transportation and air dogfighting? Its functional capability would degrade. That's why nobody does it.
Myth #3: All business users have similar data analysis needsThere is a stereotypical understanding in the BI world that there are three main types of BI users: regular users (receive specialized reports), advanced users (interactively analyze and research data) and management users (look at dashboards, monitor high-level KPIs). It's an easy, simple and misleading classification. Misleading because BI adoption is never a one-way street. Unlike transactional systems, BI is still optional. It's hard to force people to use some tool if they don't like it or don't understand how to use it. In the case of BI adoption, they can always retreat to good old Excel (and they frequently do).
People are different and they have different preferences. When it comes to data analysis, two persons doing the same task might have different views on how to do it best. A good sign of a person who knows what s/he is doing is whether s/he has strong opinion on tools needed for the job. Therefore, business users themselves should pick what they need. If business users are okay with any analytical application given to them and have no own opinion on it then they don't really need it and purchasing it would be a waste of money.
Myth #4: Business users can do a good evaluation in a 2 month period
Data analysis is a rapidly developing discipline. It's developing in many directions: methods and techniques, visualizations, processing algorithms, metadata governance, unstructured data processing, etc. The times when a BI system was simply a visual SQL query generator with some interactive charting are long gone. BI is complex nowadays, and its complexity will only increase. Even best analytical applications on the market have rather steep learning curve, despite claims about the opposite in PR/marketing campaigns. Modern BI applications can be relatively easy to start with, but as soon as something slightly non-trivial is needed the learning curve skyrockets. Look at online forums like Tableau Community, or Qlik Community -- they are full of people asking tons of how-to questions which sometimes require rather lengthy and detailed answers.
I believe that a good understanding of capabilities of a data analysis application can be developed after at least 1 year of using the application regularly on complex real-life projects. That's in a case when there was no any previous experience with analytical applications. Or at least 6 months, if there was some (which means that you should be already familiar with some concepts). Asking business users without any previous experience with BI applications to provide a feedback on an application based on 2-3 month evaluation of some demo/PoC dashboard (i.e. which are not in production use) -- is a sure (albeit very common) way to get wrong conclusions. Don't do that.
OK, what's the alternative?
Tool as a Service (a.k.a. The Data Kitchen)At this point you probably started suspecting that modern BI applications are not just more powerful than ever but also more complex than ever, and are more different from each other than ever. Comparing Tableau with Qlik makes as much sense as comparing apples with oranges. They are all round, after all, aren't they?
I believe that the most efficient way to adopt Business Intelligence is the one where adoption grows organically. IT departments should create an environment that fosters such organic growth, instead of limiting and restricting it for the purpose of hypothetical cost reduction. They should embrace the data kitchen concept, where multiple tools are available for the users who are looking for different ways to work with data. We can call it "Tool as a Service" if you will. Don't standardize on one BI system -- it's not going to work well. Ask business users what they like, and help them make it work from a technical perspective. It's the business users who should decide what to use and when. It's them who will accumulate the expertise of using the applications, not the IT people.
Practically, it means that teams as small as 5-10 people, or as big as 100 (or maybe even more) evaluate and test analytical applications themselves. The IT management should be ready that different teams may choose different applications. It's the users who should decide what works best for them. If they need two tools with somewhat overlapping features -- give them access to both. If more -- let them use as many as they need.
It doesn't mean that you will have to purchase every possible software for every user. Start with small packs of licenses for a few applications chosen by business users. Add more licenses when popularity of one of the applications increases. In this case license usage will correlate with growth of expertise. It's more efficient (also from a cost perspective) than spending millions for enterprise agreements then forcing everyone to use only the "standard" BI tool because "we spent so much money on it".