Reasons for a Restart:- The current challenge I'm playing is complete.
- Discovered I've accidentally broke the rules of a challenge after playing and saving for a length of time. However, only if I can't fix the mistake with cheats.
- Started a save in the wrong custom template.
- Forgot to change the gameplay options and/or Mod settings for a particular save.
- When testing a new challenge idea doesn't work out and needs to be tweaked.
I think that's it. I'm not counting when something drastic happens due to a glitch/bug. I simply don't save in that case and hope I haven't lost too much gameplay as a result.