Sure, but it's extra effort on your part, and there's no easy way to unsubscribe in advance - after registering for a service, should I go to the settings panel (if it exists), and dig through and make sure that I've unchecked every "hassle me randomly" box?

What I've found is that some companies will invent whole new mailing lists which are opt-out so you get the spam mail and have to log on to the site to unsubscribe. It's like playing Whac-A-Mole but for email.