I can tell you that a friend of mine did this, also in a bathroom - so far so good. I'm sure it wouldn't be generally recommended (but it does make things a lot easier)
Yes - we did this. One thing to point out - as you are "raising" the tiles (and depending on how thick your tiles are) the door frame / skirting boards may now be flush with the wall. Not a big deal for us but might upset some people!
Our tiler did this very successfully, as the old tiles were cemented directly onto the blocks, when the house was built in the 50s and removing them was a nightmare. As someone has pointed out, the finish is not as nice around the door frame, but I think it looks fine, but maybe that is just in comparison with what was there before.