I've read that I should use email subaddressing when registering for web sites. For example, if my email address is user@domain.com, then, when registering for somesite.com, I should use the email address user+somesite@domain.com.
How effective is this at controlling annoying emails from somesite.com (or, in the extreme, outright spam)? What is to prevent somesite.com from stripping the +somesite tag and sending directly to user@domain.com? Is email subaddressing something that I should bother to use, or are the benefits limited?