Pi Bonds stopping rotations

[405993422]

I understand that pi bonds stop the rotation of bonded atoms due to the double bonded/side overlapped nature but why would bonded molecules with the ability to rotate need this ability?

[Beverly Lauring 1L]

Sigma bonds allow rotation around the bond axis, while pi bonds restrict rotation due to the side-to-side overlap. Maybe they need this ability in order to react with other molecules or it can affect its reactivity.