Well System Restore only restores the system, not your personal files which should always be backed up. System restore also frequently only goes back a few days and is not really a replacement for a full system backup.
So depends on what you meant by "backup". You should always backup all your personal files, email etc. Personally I don't care as much about backing up my system, I have almost never had to reinstall windows without wanting to due to hardware or version upgrades. So I don't actively backup the system, just my data, but that's me.