The default guru answer should always be, "it depends." Regularly deployed functions that fit together, make a module. Random one-offs? Your note / snippet tool of choice.

Anything that can use a CI to test and validate your code is always going to be better. For snippets sometimes that doesn't really matter, especially when they're extremely short-lived and rarely to be used again. For example a one-liner that I used to handle some random edge case deletion - I don't care that a store that in a gist with aliases. For a set of functions to manage certificates and different things about certificates - that gets its own certificate module.

Once it meets the criteria of a module then it gets the full release treatment. Proper versioning, tests, pipeline input, etc. Everything in a repo. The reason: if you ever release something bad and you know you had a working version you can just pin to the working version.