To me the coolest thing about rocket engines from an engineering perspective is the tyranny of efficiency that the physics mandate.
Because weight is so critical, there's no luxury of "another component". If something can be repurposed, it is!
And the power opportunities afforded by continually dumping that much fuel through are mind boggling. Even regenerative cooling with combustive fuel blows my mind.
I show someone and then I tell them, that's not the rocket exhaust. That's the exhaust for the engine that runs the fuel pump for the rocket.