yes its a system to sent BTC where you need 2 out of 3 people involved in the transaction to approve it, meaning noone can run with the money alone.
Sure gp selling is maybe not that common here right now but if such a system would be added, why would anyone trade gp elsewhere?
Would attract new people since even if OSBot (only really "trustable" mods who have access to payment details should have access to the multisig system) "scamquits" they wouldnt be able to take the money. So pretty much the only realistic scenario where a scam could happen would be when a Mod scamquits and has a partner sell stuff via multisig and then gives his partner the money.
It can also be used to create a MM system that has next to no chance of a scam happening