Question on database and plugin cleanup

I just re-designed my wordpress site with a new theme.

We disabled a ton of plugins ( like forums and buddypress )

My question:

When I delete these unused plugins, does it delete any SQL values ?

Because right now, I have many rows that are dedicated to buddypress or the forums which I don't need anymore.

I wonder if these are causing any efficiency issues ?

Should I go in and DELETE some of those tables in my database ?

Thanks.