you wont wear your clutch if you 'rev-match' when doing the engine brake. Riding the clutch for too long when performing an engine brake is the common mistake drivers make. By doing this, drivers tend to use the clutch as a brake and or at the same time with the brake pedal. REV-MATCH and you wont have to ride the clutch longer and performing REV-MATCH will make it easier for your engine and, tranny.

And yes, fuel consumption will be affected (if you do it often)

Quikie info on REV-MATCH:
the simplest thing to do is just blip the throttle
basically say your in 4th and you wonna shift to 3rd
clutch in, step on the gas half way ish (after a while you'll get a feel for it) and release the clutch
that way when you downshift it'll be easier on the tranny plus the ride will be smoother.

When going to lower gear, clutch in, throttle to appropriate 'rev-match' according to which gear you are going into, release clutch.

You usually do this when you're about to do a turn or something, or when significantly decreasing speed - rev-match is used to keep the ride smooth and apply less strain on the transmission, engine, blah blah blah. (so it don't jerk so much, get it?)