I don’t know why it would be standard to use the clutch any more “gradually” on a motorcycle than on a car. Maybe there is some advanced technique I don’t know about, but I use the clutch on my bike in pretty much the same way I do the one on my car.
I wouldn’t say the clutch in a car is “on-off”. You need to gradually let out the clutch in order to get moving from a dead stop, just as you do on a bike. “Gradually” means a period of a second or two, as you are smoothly engaging the clutch while adding power.
When you are shifting between gears, it is not necessary to be gradual with the clutch, especially once you get the timing of the gear engagement / clutch engagement set into your muscle memory.
The big mistake most people make while driving a manual transmission is using the clutch to get the engine up to speed when downshifting. For instance, if you are on a highway with a speed limit of 65 and enter a construction zone with a speed limit of 30, you might want to downshift from 6th gear to 3rd gear (for example). Some people will simply put the clutch in, let the engine fall to idle RPM, jam the gear selector into third, and let the clutch speed the engine up to the correct RPM for 3rd gear. It is far easier on your clutch to rev the engine up to the correct RPM using the accelerator pedal first, and then engage third gear and let out the clutch. Somtimes it can help to slightly overshoot the required RPM, to allow for the slight decrease that will occur before you let the clutch out.
Some people take this mistake a step further and intentionally use the resistance of the clutch speeding up the out-of-sync engine to slow down the car. This is a misguided attempt to prolong the life of the $100 brake pads by wearing out the $1,200 clutch instead.
On the other hand, it is perfectly okay to downshift properly (matching the engine RPMS correctly before shifting), and then use the resistance of the engine at high RPMs to slow the car. This is necessary when descending a large hill/mountain, for example, and doesn’t result in significant extra wear and tear. It is pretty much pointless if you’re just braking on a flat road, however.
If you want to be really fancy, you can perform “double-clutch” downshifts, which will prolong the life of the synchronizers in your transmission as well as your clutch. A perfectly-executed double-clutch downshift will result in the gear selector moving smoothly into gear without any resistance whatsoever. Google for details.
This thread is going to be a disaster area anyway. Most people just don’t know what the fuck they’re talking about when it comes to cars, but they’re usually very confident in their proclamations because that’s what Daddy told them (of course, Daddy didn’t know what the fuck he was talking about either).