As a marketer, one of the issues I run into is to subscribe someone, who filled a contact form on my website, to an email automation series (usually to nudge them towards taking an extra action while we scramble to get back to them). Problem is, once the user filled up the contact form to make an enquiry, he is unlikely to go to his/her inbox to confirm... a subscription link. I do think double opt-in is the way forw…
Previously users entered their email just once, and had to confirm newsletter subscription via email. They didn't need to fill in a second form or anything, just confirm they wanted to sign up by clicking a link on an email they get.