Some people don't go anywhere without make-up so I can understand why they'd want it in a situation where a LOT of people will see them. I don't wear much generally, but I do get zits and like to cover them up. I went off to both my labours wearing the make-up I'd put on that morning. Of course 12 hours of contractions later there wasn't much of it left!
I actually had both babies by EMCS after long labours, but the second CS was supposed to be elective - I went into labour a week early and missed it. I was planning to wear some nice, flattering make-up to have that ELCS. I wanted it to be a calm, controlled, and less panicky experience than my first birth. Didn't get what I wanted, but it would have been nice.
Agre with others that you look shit after labour and will most likely end up with photos that show this! I have one of me, newborn DS and DP. DP looks lovely, adoring, happy, he had turned up at the hosp after being home overnight and having a rest and a shower. DS of course looks beautiful, and tiny. I look the size of a house, spotty, exhausted, terrible hair, massive double chin and boob hanging out of nightie. :o
Of course the baby is what matters most but I actually think the OP has raised something that does matter. Birth is a time when everything changes, when you go through the most shocking physical and emotional upheaval. It's important to do things that help you "hang onto yourself" IYSWIM and make-up may well be one of those, for a lot of women.