Git-based dependencies allow you to point a dependency to a git repo, including specifying a branch, ref or tag, and provide important benefits over path-based dependencies:
# Cargo.toml [dependencies.my-private-crate] git = "ssh://my-repo.com/my-private-crate.git" branch = "master"
One key benefit of git-based dependencies, compared to path-based dependencies, is that Cargo can fetch the source code from git on its own if it doesn't already have it. Also,
cargo update will prompt the latest changes to be pulled from origin, providing a (relatively crude) form of acquiring updates.
Assuming, in the context of proprietary crates, that the git repository specified requires authentication, this method also poses more complex setup requirements compared to path-based dependencies. CI or other automated deployment tools can often present challenges for securely providing credentials to Cargo to be able to pull the code from the repository, for example.
The most significant drawback of git-based dependencies, when compared to using open source crates with Cargo, is being forced to choose between a "moving target" or a potentially stale fixed point in the code history.
For example, if a git dependency is anchored to a branch (say, "master"), whatever changes that are pushed to that branch will be pulled and used by Cargo, without any semantic versioning-based logic to determine whether those changes are breaking.
With a bigger team and many, frequent changes being pushed to primary branches,
cargo update can become a pretty dangerous operation, at least when compared to the experience you get upgrading open source crates hosted on Crates.io. Often, this leads to a reluctance to perform
cargo update and a growing gap between the versions in a crate's
Cargo.lock compared to the newest available versions.
See also: Version Branches