Originally Posted by Nemaides
1. If I Install an older version and root using towelroot...
Would I be able to keep my device up to date with the performance updates Samsung releases?
2. These custom recoveries/kernels that would trip Knox? What do they mean and what advantages do they have?
3. If I do end up tripping Knox, can I un-trip it?
That is a lot of questions so cursory answers. You ought to do some more reading, sticky threads at least so that you have a better understanding of how everything interrelates. Not to mention that these questions have been asked and answered numerous times in existing threads.
Updates inevitably break root, so if root is important to you, you shouldn't be accepting automatic updates. We find out ad hoc what each update does after it happens. Best to watch how it affects others than be an early adopter. In the alternative, you can buy mobile odin pro or super su pro both of which have a feature that attempts to regain root after an update. No guarantees though and no one knows in advance the result.
A custom recovery e.g. TWRP, CWM, etc are full featured recovery modes that will do 100% complete backups which are invaluable. As well as provide a file browser, command line interface, permissions fix utility and other features that all work (well 99% of the time) even when something has rendered your device incapable or booting normally. Also the ability to easily install custom ROMs. Having easy and complete backups is the killer feature IMO. Soooo much better than something like Titanium. And custom kernels add a ton of features. Read the forum for extensive elaboration.
In any practical sense you have to consider the Knox flag irreversible. It's very difficult, almost impossible to reverse. Perhaps that will change in the future, but for now consider it irreversible.