Power of Snapshots in WM

Shrink operation decreased total virtual disk size to 40 GB, the gain was 14GB . Now first thing to do is take a snapshot of current state.
My main purpose is when i make irrevocable mistakes rolling back to previous snapshot; e.g: before and after database upgrade for test purposes. In addition, it can be usefull when i have different versions of database as snapshots on same virtual machine.
I upgraded my oracle instance from 10.2.0.1 to 10.0.2.3. And finally i upgraded to 11G R1.
Steps i followed:

• Read upgrade docs. from tahiti,
• Take snapshot of current version of oracle,
• Install new oracle software,
• Take snapshot of current state:previous version of instance with just new software ( before upgrade snashot)
• Upgrade instance to new version.
• Whenever irrevocable error occurs i roll back to previous snapshot.
• When upgrade successfully finished, i uninstall previous oracle software.
• Take snapshot of current state:new instance with new software only (after upgrade snapshot)

After all i have 5 snaphots so far. Now i can practice on 10.2.0.1 or 10.2.0.3 or 11.1.0.7.0.
My virtual machine now accoupies approximately 57 GB for all three versions.