There seems to be a HUGE misunderstanding here. Weight is not just used for volume, it is used to produce a better sound.
If you throw a hammer at a string, you have to release the hammer in order to throw it. The hammer will deceleate the second it leaves you hand, due to the friction of the piano mechanics etc...
If you push the hammer, you will be pushing it into the string, and produce a much fuller sound. Even in PPPPP sections, I use wieght if I want a full sound, as pppp is just soft, but still doesn't mean hollow.
I use weight most time, for many reasons.
1.....nicer sound
2.....Easier to play
3.....Takes strain away from fingers
4.....Bigger dynamic range
5.....Much more sound possibilty's
If you can't hear the difference, you need to get a teacher who can demonstrate and teach it properly, or seriously develop your ear.