Lots of RP opportunities. I mean, come on, just sitting around shooting rocks gives you lots of time to chat with other miners, Keepers, escorts, etc. Trading lets you do that with... well if you're lucky an escort, or a fellow trader who happens to take the same route.
I would have to buy some cheap, low-cargo transport (Heron?) and start TRADING with that thing, since I only have enough cash at the moment for a LH GS (which I wanted to buy).