Is OSI approval important?
which is a great — and important — question in its own right. So, is OSI approval important, and if so, why?
The OSI themselves released a proliferation report about a decade ago, describing three main issues.
Too many options make it hard to choose a license. As we see here, choosing a license is important, and an intimidating list may increase the barrier to choosing one at all.
Licenses interfere with each other. Not all licenses are compatible. This makes it hard to mix and match code, and this scales badly as more licenses are added.
It's hard to understand the overall combination of multiple licenses. In some ways, this is an extension of #2. Even if you do figure out how all of the licenses work together for your project, it's hard to communicate the total impact to your users.
#2 and #3 are the big deals to me (partly coming from my perspective working in the Fedora Project, and partly coming as a long-time user of open source). Fedora tries to be very careful that our users can trust that the software we distribute is licensed correctly and can, in fact, be distributed. Every new license adds to the very real expense of analyzing the interactions. Take a look, for example, at Fedora's packaging guidelines regarding licensing, and then at the main licensing page for Fedora. Maintaining this documentation is a considerable effort and expense — let alone actually applying it.
To this, I would add: writing a license is hard. While they may seem to be written in English, licenses are actually written in legal code, and various clauses which may seem clever to a programmer may in fact present problems. Perhaps most famously, the clause "The Software shall be used for Good, not Evil" in the JSON license sends lawyers into a tizzy, and fair enough, because who gets to decide? — if my daughter were to be asked, she might include classroom testing software under "evil". Check out Fedora's list of "bad" licenses for more examples.
The OSI list is quite large, and something from the list should cover all reasonable open source situations.
And finally, while "open source" does not enjoy trademark protection, if the open source community sticks to a reasonably strong definition, it helps prevent companies from calling software which does not respect user freedoms in a meaningful way by this label.
In addition to mattdm's excellent writeup of OSI and the issues with license proliferation, I think there are simple, succinct reasons for using OSI licenses and getting new licenses approved by them:
OSI is the go-to site for choosing a license, comparing licenses, reading the license text all in one place.
OSI is a neutral organization: just the facts, ma'am. No spin or bias.
OSI-approved licenses meet an arbitrary set of criteria as set forth by the ill-defined "free and open source software" community.
In other words, OSI is a really good repository of licenses that are heavily used by the community.