I prefer mechanical keyboards for the same reason I would prefer weighted keys on a keyboard: kinesthetic feedback. A weighted key gives you more direct feel of the balance of the key as it moves, which allows you to worry less about the complex muscle movements, and more about the actual music.

But how would forceful typing be more energy efficient? You press harder (more muscle activation), keys travel longer (more muscle activation), and you have to move your fingers back "up" again.

Btw. the reason pianists want weighted keys is mostly because it mimics acoustic pianos. If you practice on non weighted keys and play on a piano, you would tire your fingers very quickly. Apart from that major reason, the weight gives a tactile feedback when playing that is arguably necessary to play beyond what you learn the first few years. Without it going back and forth between soft and loud requires an entirely different feedback mechanism.

But this does not IMO translate to keyboards. You're interested in the tactile feedback of the "click" that signals that the press has been registered.