The difference is pressure - you have to be used to typing softly on newer Apple keyboards or else you'll soon get pain from the low travel.
Learning to do so can be very rewarding, since the low travel allows a very fast keypress. Typing softly in general is great for finger pain, and mechanical keyboards allow one to use more force but retract before connecting with the keyboard's backplane (bottoming-out in keyboard-speak) and causing the louder "clack" after the initial actuation.
Cherry MX Red switches require less actuation force than an Apple keyboard. A Red will take 45g of weight to depress, while an Apple seems to be closer to 60g [1].
Exactly. The difference is those switches allow a wide range of force, from 45g up, as long as the typist is quick enough to retract before hitting the backplane. Kicking instead of pushing.
Apple keyboards are too low for that to be possible (without some finesse), but for me ~60g is just fine.
Because you bottom out. With some practice, you can use a mechanical keyboard with never hitting the bottom because you can tell when the key engages (e.g. with a click or change in pressure). Some people believe this can reduce stress on the finger.
Learning to do so can be very rewarding, since the low travel allows a very fast keypress. Typing softly in general is great for finger pain, and mechanical keyboards allow one to use more force but retract before connecting with the keyboard's backplane (bottoming-out in keyboard-speak) and causing the louder "clack" after the initial actuation.