You learn a different technique, including sometimes less fast, less tight corners.

The fixed gear trains you better on the range of cadences, more so than the freewheel single speed, and when you become accustomed to it, it physically feels better. On a single speed I like being able to go downhill without concentrating on the speed, keeping my feet on the pedals. When it's fixed gear, I like the immediate and direct feedback, and overall prefer the fixed gear. It's something you have to try out, rather than imagine, to know if you like it.