An app that fails with the update, whether security or full OS. Or misconfigured settings.
BxActions was just updated for... bug fixes and "stability".
Some developers wait to do final testing and make changes after, not before, as things are in flux and it can be a waste of time.
One or two people complained on finding that a favorite app was not being updated. Google gives advance warning that apps will no longer be supported (2020) if they are 32-bit. Libraries will change and require rework. Permissions will be handled more closely.
Pie makes security changes. Some issues that exist will only be addressed with 9.0 and above.
IF there were problems already, an update may not be best bet or solve some issue.
Clearing cache before and or after always seems helpful though. And a boot into safe mode - does it insure things like a chkdsk would do?
Unlikely anyone is low on storage space but that use to be an issue.
And any restore is also a reason people run into trouble. If you use SmartSync with a PC the Samsung drivers now require, I think, Windows 10 (definitely not 7) if you plan to backup to PC. Makes restores fast and simple.
I tend to join beta program and will have to factory reset once - twice during Oreo beta.
Every desktop I've used runs smoother after the proverbial clean install. Not required but hey, it's a once in a year thing usually.