I ALWAYS press. I didn't pre-wash at first, then read that I should so did, then read that I didn't have to, so stopped.....so now I do and I don't, depending on the fabric, the colors (I'm pretty sure I've made a quilt with reds that will run when it's washed but too late now, it's done) and my mood and energy level.
Making clothes for years, I learned that pressing makes all the difference. I didn't always do it then, either, but the clothes went together ....and fit.....so much better when I did press. In my opinion, it's just the way to go.