Don't use it for additional time spent working uncompensated! Your commute wasn't paid for (typically), so don't give that time away to someone else for free now that you're saving it.
Personally, having a long bay area commute, i now use that time instead to sleep in AND go for longer walks with my dog, that we’d usually reserve for the weekends
Your employer doesn't directly pay for you to go to school, but most people would still see that work eventually pays for education.
Commuting is similar.
But I agree with the gist: if you figure out how to be more productive, eg by doing some task faster or by eliminating your commute, there's no moral obligation to hand over all the gains to someone else.
