An interesting question. I've done this for 3 years and the car is fine with it. However, I don't do it just for slowing down approaching, say, a light.. I use it more for engine braking. Particularly when approaching a bend at speed, wanting to go through the bend in that gear without the box pointlessly changing up, and accelerating out of it in that gear.
Essentially the same as a modern button-operated auto then, but with a lever instead.
It is not for everybody though.. if it feels right doing it, and you can do it well, it is very effective and nearly as good (in some cases, better) than a button-activated tiptronic/steptronic automatic.
For those that don't understand what I'm talking about, well, it wouldn't seem right to you, would it!
Likewise bringing the revs up when changing down.. the abillity is there, and gels very nicely when it works.
I believe the Mercedes engineers designed all this into the cars (it wasn't sometimes referred to as the best automatic in the world for nothing).
As for the longevity.. changing down without bringing up the revs produces quite a jolt, which can't be good..!
peace
Russ