Obviously the important thing is to let off of the acceleration, during the upshift or to wait on less decceleration on a downshift. Its harder on the dogs, if the motor is under a load one way or the other. Mis-timed shift can be the hard part on the tranny. Transmission problems suck, so i just give the clutch a quick pull, but I do alot of non-clutch shifting on our yz125. I put the magura hydraulic clutch on the 500, so its easier on the forearm. The pull is so fast during a fast section that I'm not sure its much different. Possibly faster shifting with clutch, since the load is takin off of the motor with the lever instead of rolling off the gas. The throttle movement is much less when aided by the clutch. Maybe its better on the transmission to use the clutch during aggressive riding and OK to not use it during a medium to slow pace. I have no experience fixing transmissions, just some shifting them.
KTMEXC125, its just dangerous to ride without any clutch. I have had to ride from a crash back to the truck without a lever and its not fun. You can't ride for fun. You can ride it for transportation from point a to point b, but it sucks. Its like deciding to ride without brakes. You think, no biggie, I'll use the other brake, then when you need to stop, your reactions have you stomp on the pedal, even though you know it won't work. Motosport Outlet will 2-day that to you for no extra charge. Their list prices include tax, shipping is free on orders over 150 or 200.(it changes)