Originally Posted by Darkgenerals

I should add, you can always add one to both sides. Wire length wont play to much of a role in this. Its not like your going to setup your cap 2 feet away.

A capacitor on the battery side, helps smooth out voltage input to the ESC.

Adding a capacitor to the Rx helps with any voltage spikes from a servo over working the BEC. This is why people install glitch busters with Savox servos. Savox's are power hungry and most built in BECs are not built to handle the loads. This is not true in every circumstance but its a good rule of thumb. Alternatively installing a high quality BEC will usually solve most glitches stemming from a servo.