What is the use of Alias Record in Route 53

As per DNS restriction we cannot point an CNAME to APEX (postsbylukman.com) record is not possible. 

Apex Record Sample - postsbylukman.com (sometimes called the "root domain" or "naked domain")

And www.postsbylukman.com is not an APEX record

Possible : www.yourdomain.com CNAME some-id.ec2.amazonaws.com

Not Possible : yourdomain.com (awspostsbylukman.com) CNAME some-cnameaws.com

The reason is DNS RFC requires "zone apex"  to be an "A Record," not a CNAME. This means that with most DNS providers you can setup a subdomain CNAME to point to EC2, but you cannot setup your root domain as a CNAME to point to EC2.

To Avoid this only AWS come up with a record a ALIAS record.