It's there to help protect the camera lens in shipment - even if there is a hole in the middle (some not), take it off for best camera function and clarity - why would you leave it on?, unless you never ever use the camera!
Just keep the lens clean and don't slide your phone camera lens on a hard surface! - heck if you have to, use one of my kickstands to keep your lens from scratching on the surface if you like to run naked or use some type of case on your phone to help lift the lens from hitting the surafce when you lay your phone on it's back.