What should I publish in crates.io?

There are a lot of awesome crates in crates.io; there is also a lot of spam and useless/abandoned crates. Is there some guideline on what does the community expect about the crates in crates.io?

I am working on a small library that will only be useful to the 50ish people I work with. Publishing it in crates.io could be convenient, but it could certainly live as a simple GitHub repository (which can still be added to the dependencies). I don't want to contribute to the pollution of crates.io so: How do you decide when/if to publish to crates.io?