It's up to you. If you don't mind setting up the phone as if it's fresh out of the box each time, you don't need to restore. You'll have to load your apps, settings, accounts, etc. If you use iCloud, and depending on how you have them set, a lot of that info should come back (contacts, photos, etc.) Restore would put all that back for you as if it was the same device before you updated, but sometimes it can bring a nagging issue back (if you had one to begin with). I've not run into those kinds of things, but YMMV.