That un-used section of tire that remains un-scuffed on many bikes is useful for a visual inspection aid. Many bikes have saddlebags and or large fenders making it hard to see the tires at a glance. Once you identify, it can be used as an early warning low air pressure indicator unless you did some extra high speed cornering and wore it away. It is also useful to determine ones riding skill's that may be riding with you to help govern the speed so you don't bring them into a corner over their head and ruin your ride.

I took this pic after installing a new tire to show how easy it is to see.