If you're developing a library, it's pretty important to specify dependencies with ^ rather than using a specific version. Otherwise, if there are 2 libraries using the same dependency, but with different specific versions, then end user will not be able to use both of them in the same project.

If you're developing an application, it doesn't matter that much. You rather even want to have reproducible builds in CI and for your teammates, but for that it's just enough to keep pubspec.lock file in the repository. With that, you will have both advantages: reproducible builds with fixed dependencies and easy upgrade with just pub upgrade command.