Leader abilities for non leaders

Adds GP, if they are a crew member will also add a bit of GP to the ship.

So...depends if you use them for ship battles or have tons of ability mats.

Gets rid of the little red icon over their head all the time. Helps my sanity sometimes

Ships is the only actual combat thing it will help, if they're a pilot. Otherwise all it does is raise your GP, which helps a small amount in Territory Battles. Otherwise, nope, nothing.

Personally, I go for it if I've got plenty of the type of mats, don't bother if I don't. Which means that for a long time I stopped leveling leader abilities I didn't use at 3 (except for pilots), and only recently have I wound up with such a surplus of mk 3 mats that I've taken them to 7.

Only if they are a pilot and you use their ship.