Advantages:
more available wing area for generating lift
more available wing leading edge/trailing for flaps/slats
places the engine weight on the wing and provides a degree of bending relief
on 4 engine types, the greater engine spacing provides less chance of an uncontained engine failure damaging the adjacent unit or the airframe
in the event of an engine fire, the wing has some degree of protection
easier/quicker engine changes and maintenance
Disadvantages:
the offset thrust line creates a bending moment on the wing at high thrust
the offset thrust line creates a pitch-up moment at high thrust
the additional distance from the centreline creates a significant yaw moment in the event of an engine power loss
the ground clearance is reduced increasing the chances of FOD
when subject to high G loads, the moment created by the mounting pylon may distort the wing; as similarly, heavy landings
the nacelle and pylon create additional drag