This is an interesting idea, but is likely to cause problems when players create an account, create a character, poke around for 5 minutes, and decide the game is not for them.
What are the bad?
If delete account, maybe delete monsters or maybe one more small monster group, who cares?
If no delete account but no play more, character still has battle
This is only small monster to fight new character. I think it will not destroy too much.
When you have 100 new players all the days, probably you can turn off :-)
