Even though I haven't really understood the trails fully, I believe that the Spanish trail (only one I've engaged with by being a part of the Spanish speakers community) has kept a lot of the steemians to keep posting even in hard times like HF18 was, besides that I don't really get the trails, but I think in a way they unite people with likewise interests. I do not support flagging of any kind on Steemit, but I understand that the rewards can be a little more generous to the authors, but I also remember when all the trails started those posts were getting a very little rewards and most of the rewards that were given to the authors were not given on SBD but by open ledger.