The Deploy All step deploys all project versions (or packages) in the snapshot, which means that projects configured in release are deployed. Snapshot is created based on projects included in release. This is very important step to make pipeline reusable across releases. Deployment sequence is derived based on priority set on the release projects. You can additionally use project groups with more than one Deploy All step to control sequencing of deployments. For example, Deploy DB changes, Deploy all applications etc. Even thought though sequencing using priority, project groups or both is supported, it is much more easier to manage sequencing just using priority instead of using project groups.
...