When you pick Apple's new APFS in Select File System, GetDataBack prompts you to choose one or more APFS Superblocks (APSB). Each APSB represents a previous file system state, sorted by the amount of data in it. These states are also called "checkpoints".
The following information helps you choose the right APSBs:
Select none, one, or more blocks to include in the Recovery Tree. The current APSB block is already included in the Recovery Tree.
APSBs represent different file system states. Instead of deleting a file, APFS increases the APSB version number for current files, leaving deleted data in previous states. That means you can easily recover data you deleted, as long as that data was not purged yet.