You are probably thinking, I have no intention of becoming a professional pilot, so what’s the point of the commercial certificate? You are not alone. None of the pilots that I trained did it to work as a pilot, but all wanted to become better pilots. I like to call that certificate private pilot on steroids, it teaches maneuvers and knowledge areas to higher standards and higher precision so that you become a true master of the aircraft.
You should get commercial certificate because it will allow you to:
But most importantly, because it is .....FUN.....
Here is a comparison of private and commercial maneuvers
Commercial ground school is very similar to private pilot. You will not need to review anything related to instrument flying, but rather to know private pilot subject areas at higher level. In addition, the following subjects will be reviewed.
Many flight maneuvers are similar to private pilot, but with tighter tolerances. For example, slow flight is done to ±50 feet, short field landing is done within 100 feet of the threshold. New maneuvers include chandelles, lazy eights, eights on pylon and power off 180 accuracy landings. It is that last maneveur that typically requires most practice, because you need to touch down with 200 feet of the specified point.
Aeronautical experience described in FAR 61.129 is more extensive than for private pilot or instrument rating, and there are gotchas there. For example, the fact that you have instrument rating doesn't automatically mean that you satisfy 61.129(3)(i), which requires 10 hours of instrument training. There are others, and FAA issued few legal interpretations, that make things even more confusing, so make sure that your CFI understands what is needed, and more importantly, what your DPE will expect.