Each use decreases the pack's life, so it should be avoided to discharge until the lowest possible voltage (3.0V per cell). Lipos don't suffer from the problem called "memory effect" like Nicds or NiMHs so they don't need to be fully discharged before they are recharged. As a matter of fact I fly my small 3S Lipo pack (700 mAh) in a depron Ultimate since 2003 without being confronted with noticeable capacity loss. I guess, the pack has more than 100 cycles (I fly almost every afternoon at home , although I never took care to keep track.

Regards,
-Fabrizio