When you have to do absolutely maximum power, even for a short time, to avoid being dropped or join the breakaway, you need maximum advantage and may have to pedal super fast to accelerate. When straining your limits like that, foot retention helps keep things simple and on track.

When you’re not racing, a little bit less will probably do and maintaining control is easy either way. I ride single speed, too, and foot retention is not required for vigorous and safe SS riding. Nothing wrong with it, though!

Otto