If you're talking about using lipo for main power, yes, you need something to protect the lipo from being overdischarged. Usually a low voltage cutoiff is builtin to teh esc. There are add on type lvc if your esc doesn't have one.

If you're asking about using a lipo to run onboard electronics - some rcvrs and servos can handle the full voltage and some can't. Those that can't need a regulator to reduce the voltage.