snapshots and backups

I'm looking at using snapshots to take a full backup. I've been search around Google a bit and so far most of the how-to's I find are always creating a snapshot, then mounting it, copying the data, unmounting it and removing it. My question is why are they doing this? Is it because they assume they only need data from one area of the drive or is there a better reason for doing this? I want to take a full backup and leave the snapshot incase I need to restore it quickly.

~Shaun 

Can anyone answer this? Are LVM snapshots capable of being used for multiple snapshots, for use as backups?