Things people do with their discretionary effort tend to be higher quality per unit effort.

When you are compelled to do something, you need to clear the bar of the person who has compelled you to do it.

Satisficing mindset.

When you do something for discretionary effort, you're doing it largely for its own sake.

You're already going above and beyond to do the thing in the first place.

A maximizing mindset.

Volunteer effort is hard to control but very valuable.