I only use Mobile 1 syn in my vehicles.
Benefits:
Allot easier to start in cold weather, (w/o block heater) for me it had to get below -40 before engine wouldn't start.
Protects the engine in hot weather
Helps protect against mechanics ID10T errors.
(Had an oil change done and they didn't screw the cap all the way in without syn I would have needed a new engine)
Helps protect against users ID10T errors, my truck was leaking a little oil, was about 2 quarts low before I noticed it. No damage to engine.
Drawbacks:
Since syn tends to be thinner then regular if things are not 100% sealed you will leak oil.