If you create a snapshot for a deduplicated directory, and then modify the contents of that directory, the references to shadow stores will be transferred to the snapshot over time. Therefore, if you enable deduplication before you create snapshots, you will save more space on your cluster. If you implement deduplication on a cluster that already has a significant amount of data stored in snapshots, it will take time before the snapshot data is affected by deduplication. Newly created snapshots can contain deduplicated data, but snapshots created before deduplication was implemented cannot.
If you plan on reverting a snapshot, it is best to revert the snapshot before running a deduplication job. Restoring a snapshot can overwrite many of the files on the cluster. Any deduplicated files are reverted back to normal files if they are overwritten by a snapshot revert. However, after the snapshot revert is complete, you can deduplicate the directory and the space savings persist on the cluster.