The Cessna 205/206/207 differs from the 172/182 in several ways.
It is bigger, heavier, and more powerful for a start.
Without going into all the specific details, you can put it this
way. If the Cessna 172/182 is the sedan of the sky, then the Cessna
205/206/207 is the SUV of the sky.
The most important difference for a pilot is that the 300 hp
powerplant and constant speed prop of the 205-series will require
the pilot to hold the high-performance and complex aircraft
endorsements. The 172 has a smaller engine and a fixed prop, so
these endorsements are not required for it.