Creating a Snapshot preserves the state and data of a virtual machine at a specific point in time. A snapshot is not intended to be used for long periods of time or in place of backing up the virtual machine.
You might want to use a snapshot when upgrading the operating system of a virtual machine. For example, before you upgrade the virtual machine you create a snapshot to preserve the point in time before the upgrade. If there are no issues during the upgrade, you can choose to remove the snapshot, which will commit the changes you made during the upgrade. However, if you encountered an issue, you can revert the snapshot, which will move back to your saved virtual machine state prior to the upgrade.