Why git tag a blob or a tree (or a tag)?

Question

I understand how it is possible to tag a blob, or a tree, or even another annotated tag, using a git tag. I understand the architecture and conceptual design that

Answer 1

Are there any use cases where it would be appropriate to tag a non-commit object?

As you figured out. In a nutshell you should avoid non-commit tagging.

Lets say for example that you have fixed a code (hot fix) and its part of a bigger commit

Why?
since it was committed like this and only later you figured out that you need only a single file.
Now you want to mark the file (content) of this change without marking all the other content.

Sample 2:
You are going over the code trying to figure out which file caused a bug, to mark a single commit you can use a tag or a git note but to mark a single file you will use tag.

And there can some other examples as well.

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The Linux kernel repository also has a non-commit-pointing tag object – the first tag created points to the initial tree of the import of the source code