Only if they have another income source. For example: my ex said that she wanted to go down to part time work (to reduce our tax liability). I suggested maybe I should go down to part-time instead, since that would reduce our income more. (hell, I'd actually like to go down to FULL time. . . . ).

Anyway, she didn't like the sound of THAT idea. One of the many reasons she is my ex.

Of course it happens.

I knew a surgeon who chose to work half days because the marginal gains were not as good as working half days (in Ontario, so his marginal rate was ~50%).