I have done some business travel and some premium economy travel, and I have seen airlines take 40-60 minutes from "formal" boarding time to takeoff. When they require 60 minutes, it usually is a big plane and the difference between business and economy could be 20 minutes easily (assuming the seating was reversed).
I have wondered many a times if boarding last would not be better? But there is a joy to leaving the lounge and directly walking into the plane if you time it right. Otherwise you end up waiting for others to board first. Also, I could afford to be late and still get in, not so if my boarding group was the last.
These are minor luxuries, but each has some value. In the bigger scheme of things, and given that it is hard to afford business travel all the time on personal dime, I would say it does not matter much :)
When I was fat, I paid extra for first class tickets so that I wouldn't be the slob jerk who overflowed into my neighbor's coach class seat. Because of that, I had a lot of coach-mindset first-class seats.
Boarding first in first class gives you an opportunity to get some work done, to relax a bit before the plane takes off, and almost always you get to have a drink and a snack before the plane leaves the ground. It gives you a chance to put your head on straight for the next leg of the journey, or catch up on stuff before the ascent.
If you're a busy person (as I was back then), boarding first really makes a difference.