I thought of it as 'fake views and subs' when I started, but from the other side they aren't. Many of the creators who regularly participate in sub4sub threads here are excellent readers, likers, and commenters. These are the people who are with you for the long haul, checking up on series as they publish, commenting on new pages when they come out. I keep up with the comics I've sub4subbed with, and mutual authorial friendships really help to buoy your motivation to keep going.
It's not bot activity, keeping high activity on your story will help it be seen more by other readers browsing the community section, and it can give you a small boost to get over the hump towards milestone goals.
Although I don't recommend spamming the forums with dozens of sub4sub threads for the same series. Once every 6+ months is plenty - there's only a dozen or so regulars on at a time. The Tapas forums shouldn't be your only method of advertising, either, but it does help.