Multilight - "standard maya sets" are exported as a layer
I would only expect layers for "lights" and for "lightGroups" when using multiLights.
Right now, if you have lights in normal maya "sets", then they are also output, which I think is probably "wrong". We use lights within "sets" for light-linking and all sorts of things, so this will be a lot of layers and I imagine it could lead to lights contributing multiple times (both from the lightgroup aovs, and also if they are in multiple "sets").
Lightgroups are light partitions, so a light can only exist within one of them at a time, so they make sense for multilight. Sets do not.
And the scene nsi_multilight_sets.ma