Using Free/Away all day events - why?

I'm relatively new to the office environment, and am remote working 98% of the time anyway.

We use Outlook. No problem. But why do so many people use Outlook full day events to show themselves as "Free" or "Away"? Am I missing a big secret here?

Looking at the calendars of five colleagues, they all have Free all day events booked in for days they're working, and Away for days they're out... Is this purely to see who is where? Or is there a shortcut that I'm missing out on?