I'm no expert but I always rev match AND use the clutch. It's just intuitive now to hit the right rpm and it snicks right in. Also, for more extreme sport riding on the street or track, slow clutch modulation can be just what you need entering a corner at high rpm. The slipper clutch is pretty harsh and I have never felt it come on except in first gear, maybe second----letting the clutch out fast. No sir, I say the clutch lever is one of your controls just like the brake and the throttle. Might as well use it. If you're smooth, I don't see how it could cause more engine wear. Maybe more clutch ware but I'd rather replace a clutch than an engine.
I do notice sometimes when I shift fast like that in traffic the shifts sound extremely harsh.
Yeah, If you're not revving and just jamming it in fast, it's a little rough. As a rule of thumb, for normal street/highway rpm, pull clutch and rev up about 400~500 rpm just before you kick it down...it's almost simultaneous. The idea is to make the downshift as soon as you hit that extra 500 rpm. the engine spins up 500 rpm in a flash at almost any throttle position. If you are off by one or two hundred rpm, that is not the end of the world. You'll get it. Let the clutch out as slow as you need to. You can be your own slipper clutch. For high rpm downshifts, you will need to rev up more than 500. When you are just crawling along, you can just give it a quick snort for a smooth downshift.
When you get the hang of it, you might leave the throttle steady, squeeze the clutch really quick (like a fraction of a second while tapping it into the next lower gear and release the clutch quick...it's swift gear change totally smooth as long as you never let off the throttle. Sounds totally badass. Use the clutch and even a little throttle to soften into the backtorque. You'll get the hang of this by sound but peeking at the tach might be the best way to start out. More rev for high rpm, less rev for low. You'll get the feel of what the bike wants.
If you watch this video from about 1:35 maybe you will sort of get the idea of what I'm saying. Sorry about the noobish second half of the vid. this was 4 years ago. ..and I was still on and off the throttle like I was down shifting a dump truck but that old habit is gone now. You don't really need to close the throttle at all before doing the blip.