As an example, during the political campaign Individual Email List season there were banners ads all over the internet you could click on claiming you would get a free t-shirt for your favorite candidate for free. Once you clicked on the banner ad you went to a website where you had to jump through a Individual Email List bunch of hoops agreeing to get other free gifts from other companies in order to finally get your free t-shirt. So if you did everything you needed to do to get your free t-shirt does that mean you wanted email from those other companies? Not likely. The Individual Email List legality of this process is tricky and one I'd never personally want to risk.
I certainly would never want to jeopardize my personal Individual Email List integrity with the people I hope to work with in this way. The people who got on this list didn't really agree to opt-in to your email list. They may have opted in so they could get a free gift, but that isn't the same as opting in to your opt-in email campaign. That's exactly what could create a legal or technical nightmare for you. When you send out your email thinking these folks are happy to get your message you might just get a nasty surprise.
When some of the big internet service Individual Email List providers get a sudden burst of emails from an unknown sender, you, going to their clients they'll flag you as a spammer and block all your messages so no one on their service gets them. Your own internet service provider may also flag you as a Individual Email List spammer when they notice that all of a sudden you're sending a huge number of outgoing messages and they could block you from sending any email messages to anyone through their services. Both of these nasty surprises are a headache Individual Email List and can take a great deal of time and sweat equity to correct.