Research points from salvaging wrecks, chance to learn component, ship, or PDC design or star system data from interrogation, theoretically Tac intel window stuff (but I don't really know what or if it ever workd properly).
As for how often it's checked, the answer is 'once per build increment (in which the officer is doing any of that stuff)' -- so, practically never, because interrogating P.o.W.s takes a few hours each, so it's over pretty quickly.