How reliable are Nandroid backups? Anyone ever experience bugs after restoring? topic

I was wondering how everyones experience with nandroid backups are and how reliable it is. Do any of you experience any bugs after restoring? Do any of you ever have any problems going back from a touchwiz and CM rom often? (Of course I do a full wipe before restoring) I seen a few users always mention they get bugs after restoring from a backup, I was just wondering if this is just a a few people.

I have 2-3 backups I want to go back and forth from, and there are days believe it or not when I miss touchwiz lol. So going back from touchwiz and cm roms won't give me any sort of bugs or anything? I am just questioning the reliability of nandroid backups