It's simple. No need to spend 15 minutes watching a video. To make a small antenna as efficient as possible, you want to make the current as uniform as possible over the length of the antenna by using as much capacitance as possible at the ends of the antenna. That's all that this "power compensator" (their name for a capacitor) is doing. You want to use an antenna that is physically small compared to the wavelength only when you have no other choice. It's a little bit better than a leaky dummy load.