Class D amplifiers use that same trick, just at much higher switching frequencies (pushing quantization noise ultrasonic, where it can be filtered). Since transistors are most efficient when fully on/off, very little power is wasted as heat. That's what made the modern revolution in tiny amps possible.

It's pretty amazing what you can get in terms of power density these days.

https://www.amazon.com/Digital-Power-Amplifier-IRS2092S-Chan...