A CNAME is simply an alias for a host record. The CNAMEs allow you to have more than one DNS name for each host record. The CNAME points to the parameter A. So if you change your IP address in the parameter A, all your CNAME records follow the new IP address of the parameter A.
The alternative is to have multiple parameters A seen, but then would have several locations or to change the IP addresses, which would increase the risk of error. Using CNAMEs is more efficient. The most common are CNAMEs www and ftp.