Are under-desk foot rests actually worth it?

Reviewers and ergonomics communities largely say yes when your chair-and-desk combo leaves your feet dangling or your knees above your hips. Threads in r/Ergonomics and r/OfficeChairs repeatedly describe foot rests as a workaround for setups that can't be lowered enough for feet-flat posture, particularly for shorter users. They are less useful if your feet already rest flat on the floor.