Auto Detail FPS

Don't know if this has been asked somewhere else, but what does the Auto Detail FPS do?

 

if at times your fps reduces to a rate that causes a burp or stutter when it happens...
you can select a minimum auto detail fps you wish to try to maintain. (example target, 60fps)
before your fps falls below that chosen auto setting your visual details will be automatically reduced in an attempt to maintain your minimum auto detail fps setting.

 

Thanks much for the info.