Good question.

I could spend it looking at other parts of the world around me, something I don't do as much of as I ought. I could spend it thinking about whatever I was thinking about before that moment. (Of course, it's possible to do these things while still pushing the button, but as we know human brains aren't perfect multitaskers.)

(The cost is also not just in time: it also wears out the button and my hands a tiny bit more than necessary.)