AMI's EBS Root Volumes vs Instance Store.

EC2 instances come with 2 types of storages- Instance store and Amazon Elastic Block Store (EBS) Volumes.

Data store within instance storage is not persistence and may often be lost during instance stops, hardware failure or terminations. Hence, it is much used for temporary data storage.

EBS Volumes are used if you want to retain data longer or encrypt data. Data is also preserved during instance stop, termination etc.

Also, in case of any lost (very less chances) it can be backed up by EBS snapshots.