My best guess is that if you live in a 3rd world country you could possibly live comfortably just by a signature campaign, depending on which one it is though. For instance, Chipmixer which is mentioned on the thread has the capability of paying up to $300/week or $1500/month. This amount of money is way higher that Greece's minimum wage (approximately $850). Thus, if I ever entered Chipmixer, I wouldn't even have to work.

Personally, I'm satisfied on Roobet, which is paying $220/month for Sr.Members and is definitely a huge help on a monthly basis.