I heard it summarized as follows: An airplane that is nose heavy flies poorly. A plane that is tail heavy flies once.

Nose heavy can be difficult to take off and perform poorly in aerobatics.

Models generally are balanced at a neutral or slightly nose heavy position with the tank empty. That way at no time in the flight do you become tail heavy.

One test is to fly at a 45º climb and do a half roll to inverted. If you release the stick and the model falls further onto it's back it is nose heavy. If it tries to increase the climb angle or nose up it is tail heavy. If it continues on course you're gold.