In the same way that there's no absolute necessity to fill silence with speech, there's no absolute necessity to fill time with stuff. You don't need to be busy every second of every day.

Often being busy is just a cover, a cover that you're trying to make up for something. When you're being busy to show the world that you're important, that's even worse. It doesn't help anyone and only wastes time, ironically.

Being unable to not be busy (sorry for the wording) shows that you were unable to prioritize your time effectively. In other words, not being busy means you're not giving in to societal pressures, plus it also gives you the benefit of more time! So, always make time for free time!