When the ESC BEC is unstable, installing an RX capacitor will ensure stable operation of the receiver and servos.
In cars, this especially improves the steering servo feel.

Servos for large aircraft require both high output and responsiveness, so they require large currents for short bursts of time.
During intense acrobatic flying, the power line may occasionally become unstable.
By using a three-prong hub or similar to attach an RX capacitor, the power line will be stabilized and the sound will improve.