Support to have a light to influence only a few objects. This would be done by specifying a collection per object, where only the lights in the collection influence the object.
There was an initial implementation in D1985, but it is no longer used in production. This implementation was geared towards branched path tracing and sample all lights.
An acceptable implementation should build its own light CDF or tree per light collection, otherwise importance sampling will be very poor with path tracing and many light scenarios.