I switched to clipless (SPD-SL) for road cycling only at the beginning of this year. My observations so far:

1. Unclipping is sometimes a challenge in emergencies or semi-emergencies.
2. I can exert force slightly earlier in the pedal stroke (mostly when I am focusing on it).
3. I can climb out of the saddle.
4. I don't sprint, but clipless is helpful for accelerating by pedaling at a higher RPM.

I always unclip my inside (i.e., right) foot at intersections. I don't feel safe staying clipped in and holding onto a post. In my area most traffic posts are pretty far away.