Gotta love telemetry. If you have the right RC transmitter it will even warn you when your lipo's are at 20% capacity. That's when you should stop to get maximum life span out of your lipos.

and for helicopter pilots.... well.. you don't want your heli to crash cause of an empty lipo .

When you have advanced equipment rotorspeed and motor temperature would be good to monitor when flying heli's.

Check out this RC transmitter, it does support telemetry. I use the dx8 myself and loving it.
http://www.rc-heli-review.com/rc-tra.../spektrum-dx7s

Good Luck