EBS Snapshot plays a vital role in disaster management. It is used to create backups and these snapshots are at time snaps of the instance and is used to restore your EC2 instance if something goes wrong which is most unlikely but then it is very useful as if you have some very important work going on in the instance and if it fails you can restore it using snapshots.
For information on how to Restore EC2 Using Snapshot read this blog. You can find a detailed information on EBS Volume, EBS Snapshots and How to restore your EC2 instance.