most people with barges are...factions, the barge is made for 99% RP in my opinion, as you can't really go anywhere that easily with it..not to mention it's a b**** docking anywhere.
The use of a barge is simple, its kind of a mining base for a faction.
The barge gets near a good mining spot, along with miners and escorts, when miner are full, they drop their stuff in the barge which gives it to transports who go and sell it.
It can also of course, be used as an armory, although its not really the best choice.