What is `CIRAWFilter.linearSpaceFilter` for and when to use it?

I haven't found any really thorough documentation or guidance on the use of CIRAWFilter.linearSpaceFilter. The API documentation calls it

An optional filter you can apply to the RAW image while it’s in linear space.

Can someone provide insight into what this means and what the linear space filter is useful for? When would we use this linear space filter instead of a filter on the output of CIRAWFilter?

Thank you.