This reminds me of many old tagging ideas, like not tagging "unicorn" on images of unicorns from the show, only OCs, or such.
I get the idea behind it (not wanting the mundane stuff that you usually don't want to find), but ultimately I think it's misguided because it behaves bizarrely when you start to consider other cases.
To use "applejack's hat" as an example:
- I want to find hats besides Applejack's, but in searching "hat,
applejack's hat", I find…a bunch of images of Applejack wearing her hat, and that's not what I want. I want to find images of Applejack without her hat, and so if the tag is omitted when it's on her head, then I can't find these images at all.
- In one episode, Chrysalis disguised as Applejack, wearing her hat; should this be tagged Applejack's hat? This is thorny if there's an exclusion, especially since the hat is destroyed and thus the tag "applejack's hat death" must apply…it'd be very odd to tag that and not the thing "dying".
Both searching cases clearly have a point, and to solve the first with the exclusion, you would need to not tag "hat" on Applejack wearing her hat…but for the second, you would need to tag "hat" on it. Thus, there is a point to not having the exclusion.
Furthermore, the intended "normal" case is easily satisfied with a negation on Applejack. Ultimately, this goes back to fundamentals of tagging; we want granularity, to choose a tag being present or not to change the images we get, so it's best not to encode exclusivity in, as it effectively forces an exclusion on Applejack we can't get rid of, removing a choice to find images.