Have you ever been a member of a site, but wanted to sign up for another account for whatever reason? Maybe you already signed up for some freebie, but lost the downloadable file. You want to re-sign up to get it again, but it tells you that your email address is already registered.
It can be a pain to juggle multiple email accounts sometimes, so use this trick to avoid the juggling act...
Gmail allows you to place a dot (period) anywhere within your nickname, thus creating a unique email address... but all of the emails still go to your main account.
For example, if your Gmail address is firstname.lastname@example.org, then you can use any of these variations...
...and so on and so on