Having an engineer will increase the speed which the ship travels through space by a 10% with diminishing returns for each additional Engineer.
Fighting isn't their strong suit, but engineers will engage in combat when chosen as a travel companion. Their weapons of choice are Pistols and Shortswords, though these are not wielded until the engineer spots a threat.
Engineers originally improved the ship's fuel efficiency by 10% periodically when left on the ship.
Because of this, engineers would endlessly buff fuel efficiency by 10% (that is, fuel cost for a given trip is reduced by ~9.1% of its previous value). Eventually, the ship could travel anywhere for free, though fuel efficiency reset whenever the ship was upgraded.