The Use of Buffer Circuit or (Super Buffer) is to Optimize the timing (Improve timing). So for example if you face Low timing paths you can add super buffer circuit to Improve the thiming. Since sometime it is very robust to optimize timeing Closer(Timing Requirements) using the Gate normal Driving Capability.
You Can read: Digital IC desing and Analysis by Sung Mokang and Yousif albalabici its contain appendix about buffer Design.