What I got is that you should finish the projects you’re working on in the Unity version you started them in. Why is this? What problems would updating cause me?
API and functionality changes pretty regularly. You’re going to have to do some work to get the game to work exactly the same way in the new version of Unity.
The amount of work is pretty arbitrary and depends on your game and quite a bit of luck.
This doesn’t mean that you should never upgrade versions. It means that you shouldn’t do the work to upgrade versions unless you need some feature or bugfix in the new version.
It’s also a lot less work to upgrade minor versions. So if you decide to stick with 2017.1, you can keep upgrading the 2017.1 sub-versions, and just never upgrade to 2017.2.