#1 reason to stay on subscription. Access to current version software. whether it's a good reason or not will depend on your situation, if you primarily work in a non-collaborative space (eg all work is done in-house, from conceptual to final) and the perpetual use license you have is adequate, then it's not a measurable benefit.
If you work as a prime, with subs at varying upograde levels contributing to the final product, the having the latest version can ensure that you can use their material with minimal issues. If you're typically working as a sub, the current version will cause problems when the prime or other team members are not using that same latest-n-greatest.
#2 reason, access to bonus/add-ons from Autodesk that are released as sub-only. Value is probably marginal, but something may (or may not) po[p up that way that would improve your operation.
#3 -- i don't think there are any others....