A public IP address is assigned to your instance from Amazon's pool of public IP addresses; it's not associated with your account. When a public IP address is disassociated from your instance, it's released back into the pool, and is no longer available for you to use. You cannot manually associate or disassociate a public IP address. Instead, in certain cases, we release the public IP address from your instance, or assign it a new one.
However,If you require a persistent public IP address that can be assigned to and removed from instances as you require, use an Elastic IP address instead. To do this, you must allocate an Elastic IP address for use with the VPC, and then associate that Elastic IP address with a private IP address specified by the network interface attached to the instance.
Therefore the major advantage of having elastic IP is that it is persistent and associated with your AWS account.