For normal road driving leaving a car in a slightly lower gear for downhill stuff is common sense and doesn't do any harm.
I am guessing that the original poster might have been more interested in whether intentionally doing a non rev matched gearshift under heavy braking to cause extra drag is a good idea or not.
Using engine braking as an aid for enthusiastic braking is putting a lot more stress on the car.
That funny sound you hear is a little bit being ground off your synchros, you are putting a lot of extra stress on the gearbox and clutch.
Its the first thing you are taught NOT do to on a racing course.
BTW Race drivers generally don't do it - they do heel and toe rev matched downshifts. Their brakes have sufficient power for the purpose at hand and they regard engine braking as a last resort when the brakes have become very iffy.
If trying it on the road, sure it feels cool and seductive but unless your brakes have started fading, you would get the same effect by pressing the brakes harder.
One thing to watch out is that under very heavy braking from 4th or 5th gear down to 2nd you really do want to match the revs carefully, because if you misjudge things while attempting to use engine braking you can over-rev the car.
The rev limiter doesn't play a part for downshifts and you can bend valves instantly if you screw up.
My personal suggestion is that if you think you need to use engine braking because your cars brakes feel ludicrously weak, then just upgrade the brake pads, plus fluid if neccessary.