A ping can be used to change that your server is physically up and communicating across the network.
It is a small packet that is sent to the server and upon receipt the server sends a response back. Other routing information can also be determined from this packet response.
Unfortunately this information can be used by hackers to scan IP ranges for potentially hackable servers.
If a server is set not to respond to ping requests then it makes that server more secure by simply being less visible to scanners.
For this reason, we disable ICMP PING requests on all of our servers.