I have purchased a switch and realized the Joy-Cons have HD rumble according to the box and many websites. But it doesn’t feel different from the wiimotes. In fact i could say the ps4 controller rumble is “4K” Compared to the HD rumble. Does this have another function? thanks
HD rumble is essentially just another type of rumble motor (rather than the normal rumble motors that are just regular DC motors with a weight attached to the end that spins, it uses magnets to move a piece of metal back and forth in a straight line) where you can control the pitch of the rumble, kind of like how a subwoofer works. It's actually the same type of motor used in the Steam Controller (linear actuator) and the Oculus Touch controllers and I believe also the Vive controllers.
It doesn't really have any practical uses beyond that, there's stuff like the ball counting minigame of 1-2-Switch that makes good use of it, though the whole thing about it feeling like balls are actually rolling around inside the JoyCon is a big fat lie, it's just that you can tell by the pitch of the rumble how the balls are bouncing around inside. Besides very niche applications like that, the best it can do is provide improved haptic feedback, more realistic rumbling during earthquakes, explosions, that sort of thing. It's a nice little added extra but nothing revolutionary.
It's a gimmick barely used, and i hope gest removed in a new revision of the switch and joycons, so they can be cheaper
TBH, I doubt it adds much cost. Maybe 1-2 bucks per motor, you gotta remember that the Pro Controller is not much more expensive than a DS4 or a XBox One controller, in fact the price difference currently is less than $10 and the XBox One/PS4 have been out much longer and have had multiple price drops. And the Pro Controller also has NFC and gyros bumping up the cost, the DS4 does have gyros + touchpad bumping up the cost but the XBox One controller doesn't have anything like that so logically it should cost less than the DS4 but it actually costs a little more.
I think it should be the standard for controller rumble from here on out, it's just better in general. It's not game changing or anything, it's simply a superior technology and I don't really see any drawbacks to using it for everything. Maybe not for mobile phones, because space is so tight and linear actuators seem to be quite a bit bigger than regular rumble motors on average, they are also relatively heavy as they are basically just a massive piece of metal. If you look at the inside of a JoyCon the linear actuator takes up the entire width and thickness of the controller, just placed at the very bottom.