Snapshots are the snapshots you have taken of your VMware installation.
When you create a snapshot on a virtual machine, a certain point in time is recorded, meaning as of the time of the snapshot, the original files of the VM remain as they are, and all modifications are recorded in new files. This may take place during ongoing operation of the virtual machines. It is also possible to merge the current data with the data of the snapshot, which also does not cause downtime. Only if you want to delete the data accumulated since the snapshot, the virtual machine is stopped, reset to the old status, and activated again.
Theoretically you can create a large number number of VM snapshots, however, this is hardly beneficial due to the lacking transparency in snapshot administration and the elaborate management.
As soon as a snapshot is created, the newly produced Delta files grow dynamically with the activity in the guest, and every modification on the hard drive thus leads to an increase of the Delta-hard drive file. This relates to every modification, from copying a file via secure formatting of the hard drive with zeros all the way to deleting files. The drive space need is never reduced. However, a Delta file can never become larger than its original file, as all memory blocks were copied 1:1. If the same block is overwritten a hundred times, this does not change the size of the Delta file. As soon as a new block is written, the Delta file grows along with it in steps of at least 15 MB.
Thus it is important to understand that after creating the snapshot, the additional memory requirement may be doubled at most, but this is applicable to every snapshot; meaning if the Delta file is 5 GB in size after the first snapshot and a second snapshot is created, the Delta files add up on the datastore. This is why you need to watch the number of snapshots as well as their size.