Snapshots are a good way to do backup and they're great it you want to rollback from a change / patch / etc. My concern was over the size the of snapshot - i.e. 270 GB snapshot file on your 800 GB vmdk. At some point you'll want to commit the snapshot and if something screws up there seems to have been a lot of data that will have changed. Plus the snapshot will take a very long time to commit back to the main vmdk.

The vmsn file by the way is a snapshot of the memory of the VM when you took the snapshot. If you were to revert back to the snapshot then the VM would load up the memory file and the VM would start exactly as it was when you took the snapshot.