It makes sense in the sense that if someone wants to depend on your library, they will want to have some reference for what version they are using. It first of all provides points of reference when talking between developers. Even if the library isn’t being released at all yet, it’s useful for people who use it anyways, to mark “more stable” versions, and to mark before major breaking changes.
The version marker comes in hand mainly when releasing on crates.io. You can release your library on crates.io, even if it isn’t stable or feature-complete at all. As long as your version is 0.*.*, “anything goes” for breaking changes. When releasing development versions on crates.io, the versions just mark stages of development. If you are about to make a bunch of breaking changes you can bump the version so that people have a semi-stable reference point.
Personally, I generally leave the version as 0.0.1-dev until the first release I make on crates.io. After that, I’ll just release versions on cargo as 0.1.0, 0.1.1, 0.1.2, etc. These version may have any kind of non-backwards-compatible changes, and I just release them so that someone depending on the in-development library can declare that version in their Cargo.toml for a snapshot of my library. The usage of -dev isn’t as far as I know, I just use it to tell the difference between a released version and something on the git tree.
