Re: Pressed powders/compacts
It's used to set the makeup and give you a finished look (if you're using the right one). I never used to wear one and then I was converted. It just evens out the whole look. Especially for me now as I don't wear foundation all over my face. It shouldn't make you look powdery.
And yes the obvious, mattifying and touch-ups.
I use MAC select sheer pressed.