LemonWire is a P2P file exchange application, that in this case uses the Gnutella network. This client is based on others better know like
Bearshare o
LimeWire. The advantages that it offers include small disk space, and a simpler use (easy interface etc)
Also, in LemonWire you can find some options that aren`t in other similar programs, like detailed searches (with filters so that only determined file types appear), or a high speed, not only in downloading but also in intermediate processes like connecting or source searches. As ever, with all these types of P2P programs, you should try it first and evaluate the results with your particular computer.