I'm interested to know, under what circumstances would a barter system like this benefit its participants, given that they can already exchange these services u

I'm interested to know, under what circumstances would a barter system like this benefit its participants, given that they can already exchange these services using cash? The primary advantage of barter seems to be sidestepping taxes, and judging from the scarcity of successful online barter systems, that advantage is either legally unsustainable or too small to make a difference.