the clock rate is a very important comand it defines which side of the wan link will be DCE and which side is the DTE i.e. which side is goint to generate the clock , because all serial interfaces are synchronous i.e. detection is based on clocking
The clock rate is the speed at wich the data is transfered from some sender, so the receiving side of the communication must know what this speed of data is, in order to catch the bits in the moment their are happening on the line. Hope it help you best figure out how digital networks works.
yes, as i told you, the clock rate determined the speed of data transfering over the network. That means that if you have a low clock rate, then you have a low bandwith (bandwith = bits/second AND every bit transferred depend on the clock rate)