There's some skinsuit marginal gains

http://www.cyclingnews.com/news/alaphilippe-and-bernal-wearing-custom-made-tt-skinsuits-at-tour-de-france/

Close attention to details right there.

There has been talk in the past that they may be tailored, but that doesn’t make them fast.
I seem to remember a couple pros being upset that they couldn’t wear the skinsuit they knew was fast from all their teams testing, and instead had to wear one prepped on site by the tailor

Yes, good point.

Having the manufacture there to get any folds or flaps out sure can’t hurt either though.

Alaphilippe absolutely crushed that TT.