ground balancing is the fine tuning of a machine so that minerilization in the soil wont interfere with depth. in highly minerilized ground,it becomes difficult for the detector to "see" into the ground. by ground balancing the machine, you are in effect compensating for the ground minerilization, helping the machine to see into the ground better. some machines automaticly adjust the ground balance, others are manually set, and still others are pre set at the factory to deal with "most" situations. in general, it is better to have the option to either automaticly or manually set the ground balance, but in a lot of situations a pre set ground balance will do ok. so to answer your question, no its not needed, but its nice to have.
