What does the Physics Interactions setting actually do?

Lately I’ve been planning out a transmog set that’s supposed to resemble an existing character that involves a rather static, solid owl helmet. The helm I’m wearing now is REALLY close, but when I tried it on today the physics that keep the feathers and dreads bouncy really kill the silhouette.

I thought turning off Physics Interactions might help, but nothing has changed despite a client restart. So what is the setting actually for? I would’ve thought it was for all the wiggly physicsy gear that was introduced when the setting was first implemented.

I think it’s for things like grass bending when you step through it.