The theory behind Sub4Sub is that small channels can get a fair amount of subscribers quickly to create the illusion that they've brought in a lot of traffic, and more people will organically subscibe due to the popularity. I looked into it too. I've honestly met 3 creators that we legitimately worth subscribing to and we've supported each other. The rest are view grabbers, who will more than likely unsubscribe. You're better off doing things the old fashioned way with SEO, Facebook/Twitter promotion, Engagement with the community in person, commenting on other videos, and i guess maybe an Ad Campaign. It's a slog, but I've noticed that some of these Sub4Sub guys will have 1000 subscribers, but their videos have a third of the views mine get. Example, I put out one of our signature videos a few Saturdays ago. Our loyal subscribers got us 60 views, whereas a guy with ten times as many subscribers as we have, only pulled 23. That same video is now over 140 views and the other one is lost in his new random jank. So the results speak for themselves. We got ten times the traffic with 1/10th of the subscribers.
Too Long, Didn't Read: Styxie is right. Sub4Sub is trash. Build a real network with real people.