Sometimes when you subscribe, you get a discount. Or a "no more popups" message. I use unrollme to put all of those in in a single daily email.

The ones I don't put in unrollme are ones that have actual value. The rest - I don't need 4-6 emails telling me about URGENT sales and DON'T MISS NOW special offers, when they have the same exact offers the next week. If an email leads to a "click here to sign up and receive our free (whatever, usually ebook)" and then adds you to a list that leads to being added to multiple other lists that you didn't opt in on, I use unrollme to just unroll completely rather than digest the emails. Deceptive marketing is just bad marketing.

ETA: I do not work for unrollme, it's an extension a friend recommended.