Coulson and Co. have really been crippled by the absence of a scientist ever since Simmons was taken by Kasius; Fitz’s reappearance could make a huge difference.
Assuming Fitz isn’t suddenly a bad guy embracing his former Framework self, the odds are that he has some big ideas on how to rescue his friends.
In fact, given his history with gadgetry, he may be able to figure out how to get the deafening contraption out of Simmons’ ear and deactivate the devices controlling the Inhumans’ powers.
Fitz presumably has information at his disposal, and there’s no denying that he’s very intelligent.