They're not a good strategy. Have you seen anyone who regularly engages in sub-for-sub threads who has even a thousand subs? No, because it's a completely unsustainable way to build an audience.
Having visibility on Tapas outside of the forums and discord, the kind of visibility you can sustain just by updating regularly, requires you to get likes on your pages. Sub-for-sub readers are often just an empty sub, not giving likes or other engagement, because they're not actually reading, and even if you did get a reader off a sub-for-sub who agrees to like all your updates if you do the same for them... how can you keep that up on more than about 20 works or so? It's impossible, it won't work, it's too high-effort for the small number of subs you get for it.
Then the second aspect, unlocking revenue. You need 100 subs to unlock ad revenue, and 250 to unlock the ability to withdraw it... but both are pointless if you're not getting views because if your ads don't make any impressions, and nobody donates ink, you'll never get the $25 of revenue to actually withdraw anything.
Next point: Sub-for-sub is a distraction from the problems that are causing people to not want to read your work. If you post your work online and the only way you can get somebody to look at it is to bribe them with a return sub... there's a problem with your work. Something about your cover, your blurb or your first few updates is putting people off wanting to read it. People should want to read your comic or novel because it's enjoyable to read, not because they're getting paid! If you resort to sub-for-sub, all you're doing is burying your head in the sand, when you could be asking for advice on how to better present and market your work, or how it might be improved to be more enticing or enjoyable. The people here will happily give feedback and advice on how you might change things like your cover or blurb, or on ideas for how and where to advertise that might not have that immediate dopamine hit of "number go up", but will ultimately let you get so many more readers if you follow it.
I'm not offended by sub-for-sub, I'm just frustrated over here trying to tell people why it won't help them in the long run to achieve the goals they want to achieve with their work. You have all these people spending their energy making endless threads to swap subs with the same tiny pool of people, when they could spend that energy learning things that would actually help them get where they want to be.