Having actually done what @JammyDodger has said on one of my communities I strongly recommend against it unless you fully trust your users not to abuse it.
We had to return the settings to the defaults after we kept having people get upset because they did not like the responses they were getting so they would delete their accounts when they found out they could not delete their own topics.
That said, if you can fully trust your users not to abuse it, it can be helpful in some cases. 
Just one small suggestion: if you’re going to modify those settings, make sure your modify the related site settings that control when staff can delete accounts as well to be consistent.
In particular, make sure you set these settings the same:
delete all posts maxdelete user self max post countIf you set the former lower than the latter you get the curious situation where the user can self-delete but staff can’t delete the account.