Re: Software update.
Shutdown physically powers down the computer and flushes the caches, which can get rid of any bad code or corrupted background operations -- it also runs diagnostics at startup that can detect and address some left-over issues. Restart doesn't do all that so it's less likely to solve some problems, which is why when you're having inexplicable issues you should always do a full shutdown, wait around 30 seconds, and then power up again.
OS updates -- especially security updates -- can occasionally break third-party software [and even Apple software at times] -- it happens often enough that most audio/video people don't do ANY updates, no matter how minor, without waiting long enough [weeks/months] for reports of problems to surface on reliable user forums, and then doing their due diligence [research and an up-to-date bootable backup] before updating. If you want to take your chances and succumb to Apple's pushing to always stay current, then go ahead, but unless you maintain a current clone backup and know how to do a full restore, I would instead turn off automatic updates and follow the recording studio mantra -- "if it ain't broke, don't fix it".