What would you use your Masterball for?

In a game sense, I never use it because a competitive spirit inside me wants to prove I didn't need it even if it makes my life harder and I won't ever show my save file to anyone else and nobody will know if I "cheat" by using it. In an irl way, do the same as in the games, keep it for legendaries. But you should really do like Ash and become their friend instead of throwing a ball at them.

I mean when using it on a creature that is not a pokemon. If I catch a person will they have to serve me? How much control can I exert over them? Will it be possible for them to disobey or ignore my orders? If I collect enough gym badges can I completely dominate them? I'm probably overthinking something that was never meant to be thought about that hard.