I think that when you play softly you should still sink into the keys.. otherwise you're really barely scratching your face. The sound doesnt travel, and you can hardly hear yourself. Even if you're playing softly, you still want to be able to hear what you're playing - and so does the audience, especially the old lady at the back thats hard of hearing. Thats just what I think though.
I totally disagree!Playing the key only half-way down (or 3/4 or whatever) is one of the most colourful expressive tools that there is!If you only ever press the key fully down you'll only limit yourself and the nuances that you can give the music.I'm sure a pianist can be excellent anyway.But I think you're wrong about the sound; it WILL carry to the back of the hall, and you will most certainly be able to hear yourself when you play like that.There are lot's of ways you can use it: softness in accompaniment (listen to Pogorelich playing Chopin's funeral march, middle section!); embellishments; trills (e.g. try a diminuendo trill by gradually releasing the keys); for more interesting scale-passages try some of the notes half-way; delicate stacatto...etc etc.Of course, constant full depression of the keys will yield more power, but I find this constant power to be a bit tiresome to listen to. Anyway, my opinion..