Jar Dependencies

There is a small debate in the software community about whether or not it makes sense to check jar dependencies into the code repository.  Keeping them in the repository leads is a more traditional approach to managing dependencies and builds, but build tools like Maven store the jar files outside of the code repository in a jar repository.  This approach has the advantage of ever only needing one copy of any particular dependency on your machine.  The two alternative methods have me wondering what it looks like when one needs to go back and build a previous version of a project.  If the jars are stored in the repository, then its clear what jars are included in the build.  If the build relies on a pom file, is it as clear?  Are they the same jar files?  It seems like they should be as long as its a release,  but it also seems like snapshots would be impossible to be rebuilt.