The ability to share files on a very large network. It's a give & take approach. LW is at the forefront of the Gnutella network development. Rules are put in place to develop by so gnutella programs don't slow down network systems by over-querying. Thus you find you don't have to wait in long queues & can get fast results unlike some other p2p networks. LimeWire also makes some attempts to stop leeching. But not to say it doesn't stop it completely. And for people to configure their systems so "sharing" can be done.