Sure, it can be filtered out, but there are people who likes it regardless if it's from the film or added in by the studio.

I'm not an expert but I believe mostly it's there to combat banding. But then again, there aren't really that much dark scenes in Kill la Kill.

A good example would be the corpse party ova. Before gg released theirs (with grain), the copies I grabbed had banding issues. gg, on the other hand, was good because they left the grain.