not always, I have found in the past upgrading can leave things behind, restore is the one that wipes everything off. If update wiped everything you wouldn't have music after updating![]()
Updating has been known to leave stuff like apps and files from those apps on the phone, but since they're not supported, they become "invisible" on the springboard, you can however see the files browsing your phone trhough ssh.
Restoring on the other side, does wipe out everything, so that's the reason its more recommended.
It's also helpful when certain apps change permissions or move system files, restoring ensures, no weirdness will happen afterwards.
Thanks!!