You should read this
Conclusion (from the link provided):
However, the ping attribute provides these advantages to the user over those alternatives:
* It allows the user to see the final target URI unobscured.
* It allows the UA to inform the user about the out-of-band notifications.
* It allows the paranoid user to disable the notifications without losing the underlying link functionality.
* It allows the UA to optimise the use of available network bandwidth so that the target page loads faster.
Thus, while it is possible to track users without this feature, authors are encouraged to use the ping attribute so that the user agent can improve the user experience.