It's useful to set another email address. I tend to have a main email address and a second one for single use type mails (where I may have bought a one-off item online). I usually just delete most of the mails or 'unsubscribe' them. But it does keep it in use for its main purpose which is to provide a recovery email address should you be locked out of your main email. Gmail encourage you to provide another email address for this reason.
I think it's regional differences...


