Generally if you're on Evilnat 4.88 it would be worthwhile updating to 4.90. Evilnat has been adding a lot of new features to his CFW that previously required a 3rd party app (e.g. Rebug Toolbox). At the very least you will want to dump and backup your ERK and IDPS.
Also, if you wish to use PSN, mind that PSN requires you to be on the latest firmware version, and while there are ways to spoof the reported version, it is considered safer to just actually update to it if there's a CFW based on it (which there is) and there are no undesired changes (which there aren't).
Generally the changes that OFW had between 4.88 and 4.90 are:
- Updated Blu-Ray encryption keys. This is needed if you use your PS3 for watching Blu-Ray movies. It has no effect on games.
- Removal of the ability to create new PSN accounts directly on the PS3 and the ability to use credit cards on the PS3 store, due to security concerns. Staying on 4.88 will not allow you to work around this, because it has also been disabled on the serer side. You can still create new PSN accounts on Sony's website. To buy digital games and DLCs on the PS3 store you need to buy credit on the PSN account via the website or on a PS4/PS5, and then you can use it on the PS3 store.
By the way, CFW allows you to QA flag the console, which in turn allows you to downgrade the firmware back to any version not lower than the one your console originally shipped with, so the update is not a one way process.