you can't insert data in a row that has been deleted or is not there
Why not? The numbers aren't being used anymore. Seems to work perfectly fine to me. Just developing a method to find that missing number is what I can't do (without some kind of big loop)

my point is that I don't get holes like that, and it is set to auto-increment.
The point is, that mine does.

if your database is going to get real big, then why consider deleteing them? how can it get big if you delete them?
Because my site contains snippets and tutorials that users can submit. If a user submits some vulgar thing or something malicous, I need to delete it. Also if things become outdated, etc.