This might make an interesting read for some on here
TL;DR but,
My gut feeling is that a 'use your own kit' policy isn't a best fit for every organisation.
For a start, it raises big support issues. IT are expected to support any old random piece of crap they've never seen before and somehow make it work with the existing infrastructure. Now, for large organisations this probably isn't a huge problem as they've got a larger IT resource to deal with it (and by definition, a broader pool of knowledge); but for smaller places, it's a complete nightmare.
For context, In the past I've been the only member of IT supporting maybe 400 staff in one organisation, and one of four supporting a thousand in another. And by "member of IT" I don't mean "support desk staff," that includes infrastructure, IT management, everything.
Then you've got security to deal with. There are ways to deal with this (such as endpoint analysis) but having uncontrolled devices plugged into your LAN behind the firewall immediately presents you with a risk that can potentially wreak havoc.
And that's the tip of the iceberg, I could go on. Point is, there's a reason IT departments roll out standardised kit. It's so that it works, and they can keep it working. "Choose your own" can work, but it's a big ask.