[ghaff]

In fact, although it's not super-common, some US companies have official "summer hours" where they maintain a nominal 40-hour week but Friday is a half-day or off entirely (maybe every second week). TBH, part of the theory is that a lot of people take short days on Friday anyway, especially in areas where a lot of people want to beat the weekend traffic to the beach/coast/mountains.

And if it's going to tend to happen informally anyway, it's probably fairer to make it an official policy for everyone.

That said, I personally mostly lean towards more vacation days I can take together rather than every week being shorter.