I suppose I think of it as mixing the offensive/defensive thinking - if I, as the pilot, can either focus on lining up an attack while someone else on board looks for threats (like SAMs) or else I can concentrate on keeping my head on a swivel and looking for threats and moving the aircraft through the sky while my backseater focuses on making a precision attack with a guided weapon danger close to friendly forces and collateral targets one would rather avoid
Re: SAMs - modern aircraft have much better threat receivers, and automatic chaff and decoy dispensers that decide themselves when best to deploy, unlike jets of that generation which still were manually deployed (at least the earlier models)
Re: attack with guided weapons - likewise with advanced guided weapons and bombing navigation systems they have less to worry about that these days
Aircraft back-seaters now tend to be electronic warfare experts, since that is now the only operator-intensive job they're needed for, but even so modern systems on the 4.5th and 5th gen aircraft can be comfortably operated by the pilot - supposedly the F-35's electronic attack suite is even more "push-button" than that
Although they do say there may be a need for a drone operator in near future combat aircraft, to operate "loyal wingman" drones. But even those will improve in autonomy eventually.
