I used to mostly ban, but then like PJ states, you need to also ban the email and IP address and delete the users posts.
Under the advice of the admins, I started using the delete function more. It's all gone in one click, but there is no record of that user.
From time to time, I will go through the list to see new members and view what's in their signature or website to catch spammers before they can post to the forum. Go through that list sometime and see how long it takes you to sit there to ban username, IP and emails. It takes a lot of time!