That has the same problem as taking them as travel companions: most combat encounters are balanced around Steele fighting solo, and those that aren't are in a quest with guaranteed limited-time companions. That said, most crew members already have one or two functions; many are capable of crewing turret weapons (which are more powerful than their regular versions but require a valid crew member to fire), and some have some miscellaneous buff (Paige reduces travel times, Shekka repairs the ship over time for free, Anno is a merchant with top-tier sell prices, etc.)