A snapshot is like taking a picture of your virtual machine (VM). When you take a snapshot of your VM is an exact copy of the state your VM is currently in. Think of it as a back up of the system at that exact point in time when the snapshot was taken. 

Why might you want to take a snapshot?

• Quickly recover the VM at a known good state

• Prior to installing software - in case the software does not install correctly or fails to install you can go back in time prior to when you attempt to install the software. 

• Prior to doing updates - in case the updates do not work you can revert back to the snapshot you took prior to starting the update process.