In 2019, I got to carhaix at just the right time and got a shower and cot right away. Huge line for food, so I waited to eat until after I slept. The worst waste of time was the bathrooms, but apparently I was drinking enough this time so I wasn't going to leave any solid offerings by the side of the road. I think the main thing about a shower is helping your sit area recover. I had problems with one of the shorts I rode with in 2011, and I think the shower was 100 percent necessary.
There is no reason to be too rushed on PBP. If you are so pressed for time that you can't take a shower or two, you are in trouble.
I don't recommend that PBP as your first 1200k. It was mine, and the whole thing was a bit of a mystery. Of course, it has been a lot of people's first and only.