Of course you can't decide whether it's useful to the payer. You can and should ask yourself why someone would pay for it, and then decide according to your own

Of course you can't decide whether it's useful to the payer. You can and should ask yourself why someone would pay for it, and then decide according to your own personal criteria whether to trade your labor to that particular employer. It is perfectly rational to choose lower income occupations for your own reasons. Income maximization at all costs is how you become a pawn in someone else's game even (especially?) if it makes you rich.