Gonna drop some autism real quick.
Most Cookie☆ "characters" are representations of real-life voice actors. The characters they voiced are used kind of like avatars to represent the voice actors.
Visually most Cookie☆ characters' designs are based on Touhou and should be tagged as such
but there are characters whose designs
aren't based on Touhou, and drawings of the real-life voice actors themselves, and those being tagged with Touhou can be annoying and can cause confusion.
For example, on Gelbooru there is a Cookie☆ tag but it's followed by "Touhou" in parentheses.
Characters(voice actors) like Yuyusu, Kofji, and Ichigo have representations that aren't based on Touhou, and having those posts tied to Touhou isn't appropriate.
e.g [
gelbooru.com]
https://gelbooru.com/index.php?page=post&am...i_%28cookie%29+Galleries where a Cookie☆ tag is
needed is unlikely, and it could be argued that a standalone Inmu tag is enough for those galleries, but it'd just be convenient to have a Cookie☆ tag.