A big plus in Gmail: the fact that you can use a plus to create an unlimited number of e-mail addresses in one account. Just add a + and a unique word between your username and the @-sign.
If you use something like 'email@example.com' the next step can be to make a filter that adds a label automatically to all mail send to this specific address. Or let them skip the inbox. Or stick any other action you can think of to it.
Also the + can help you to trace the bad guys in advertising. If you subscribe to a newsletter with firstname.lastname@example.org, and after some time you get a lot of spam on this address... hey, gotcha!