If you're talking about working for yourself (that is, working for customers), then sure, that makes sense.
If you're working for someone else who is paying you specifically to work 40 hours, then there's no reason to work more than that unless you consider your time worthless.
If you're working for someone else who is paying you specifically to work 40 hours, then there's no reason to work more than that unless you consider your time worthless.