A racing venue may be composed of more than one circuit, and it will be useful to identify these. Motor racing tracks seem to be generally tagged highway=raceway, leaving reference to the name=* tag to figure out which part you're looking at. For instance, the main track at Donington Park has two circuits
Anyone that needs to produce a map of a specific circuit (such as Image:Silverstone_Circuit2.png) need only look up the relation to establish which ways need to be rendered. Unlike relying on highway=* alone, this would also work on street circuits such as in Monte Carlo.