Over the years, it's varied, depending on the company. My first job, they did nothing. there was no "official" early closing policy, but the higher ups would always be gone, leaving the rest of us to the mercy of our individual bosses. And mine generally wouldn't let me go, but it was ok for HER to take off early. I got to the point where I'd leave shortly after she did, as we went in opposite directions, and she had a long train ride, and this was also before cell phones. She really irked me one time; she left about 3:30, then told me I could leave at 4:30 - really? I was gone 10 minutes after her!
Until this job, it was alwasy either last minute, or at the bosses' discretion, which we know doesn't always go well (see above).
In my current job, initially, our president wasn't really interested in anything but himself, so he'd be out, so he couldn't be bothered with the rest of us.
our current prez, is a whole other ball of wax. Pretty much every holiday we get an email several days before, and we normally close at 2 the day before any major holiday, NY Day, Thanksgiving, Christmas, Memorial day, 4th of July and Labor Day. Additionally, we have a half day the last day before Christmas, so if Chrismas Eve is friday, we'd be off, and have 1/2 Thursday. Which is nice as we can plan ahead.