Snapshots in Virtual Machines are a great idea. They allow you to test out changes safe in the knowledge that you can revert if necessary, without any clutter left behind from an uninstall. They are brilliant for that!
This post comes off the back of seeing many people using VMWare snapshots as some form of backup system. DO NOT DO THAT!
I cannot stress enough that a VMWare snapshot is not a backup at all. The snapshot is kept in the same location as the main storage files, so if you lose the storage that your main VM is kept on you also lose the snapshots.
If you want to use a VMWare specific method of backing up you need to be looking at exporting your VM as a template. You can then farm that off to some safe location and use it to restore if necessary.
Unfortunately this is not explained well by VMWare at all, leading to all sorts of confusion and people using the technology for the wrong purpose.
Added to this, when you have a snapshot VMWare stops using your primary storage file and starts writing the changes to other files (delta files). This results in you using a lot more storage than anticipated and also puts a much higher load on the I/O system.
To conclude, snapshots are great, but use them as intended, for a short term to prove changes in a system. Once you have done that, delete them quickly. The longer you leave it the longer it will take, as VMWare has to merge back in all the delta changes to the main storage file before removing a snapshot and this is SLOW!