In certain cases you might choose to reclaim space on the cluster by removing old snapshots. Nutanix files takes two types of snapshots.
External snapshots: The external snapshots are taken by the files protection domain (PD) which takes the snapshots of the whole Nutanix File server.
Internal snapshots: Internal snapshots are the snapshots taken at the share level which leverage ZFS directly. It can be the Self Service Restore snapshots or the third party backup snapshots using CFT API.
If need be, the external file server PD snapshots can be removed directly from the prism UI -> Protection Domain -> local snapshot page.
The internal snapshots can be removed using the afs command line utility. If you choose to remove the internal snapshots the following KB article walks through the step by step process along with the afs commands needed.