A FARP (Forward Arming and Refuiling Point) is a temporary field base set up relativly close to front lines. It's primary purpose is to remove the need for a gunship to return to an airbase to perform a simple rearm and refuel run. Once the area is no longer a combat zone, or operations are ceased, the equipment and personnel used are sent elsewhere.
The primary intent is to increase turn-around time for helicopters. By not having to travel a long distance back to an airbase or carrier a gunship can remain in combat much longer.
However most FARPs are not equipped to handle more than light maintenance, so a damaged helicopter would have to be routed to a real base for repairs. Also, helicopters are rotated between the FARP and a base to keep the ones in the fighting, flying well.
FARPs are also generaly not well protected, and rely on their low profile as a stealth protection against attacks.