A build can be pinned to prevent it from being removed when a clean-up procedure is executed, as stipulated by the clean-up policy.
To pin/unpin a build:
on the Build Results page, select Pin in the Actions drop-down menu, or
on the Overview tab of the Build Configuration Home page, select the Pin build action
The Pin/Unpin build dialog also allows you to tag the build.
If the current build is a part of a chain and has snapshot dependencies on another builds, the "Apply to all snapshot dependencies" box appears. Check this box to apply the actions (pinning/unpinning, adding / removing tags) to all dependency (preceding) builds of the current build.