Not necessarily just for that. It's also useful for people knowing whether they send you something Thursday towards the end of the day that's somewhat time sensitive whether to expect/hope you'll get to it, or if that's something they shouldn't expect any more than sending it towards the end of the day Friday. It's useful in the same way as knowing when holidays are and not estimating when someone might get something done while including a Monday they will not be working.
I feel like many or most places already have the "be cool late Friday" mindset. Emergencies or critical things can still happen, but if possible maybe don't schedule a long meeting end of day Friday. Don't ask for something that needs turn around after the morning as people already are going to likely be in a wrap-up mode. It always feels like a very implicit "can this wait till Monday?" attitude permeates the day. And it's not just being nice, splitting a task over a weekend can lead to things being forgotten or missed or just the context being lost. Hell, I've seen places operate more in a "be cool all of Friday, it's the pseudo-weekend".
All that is a long way of saying that that group feeling now exists a whole day before and it's important to communicate that.
Not required, but useful.