I'm not sophisticated about Google Analytics, but I use it to track basic performance parameters for my website. I've created custom filters, to exclude data from referrers which have no genuine relevance to my business. Now I see a message in Analytics which says I should delete unusued filters, because they are "not applied to any views". This is confusing, because the filters are applied to my principal view, and they are effectively avoiding distortion of the data which otherwise results from traffic originated by spam bots, etc. Why am I receiving a message which says the filters are not applied to any view?