Synchronous data transmission is used within the motherboard where the components can easily be kept synchronised data is moved reliably and almost always arrives at the intended destination.
It provides a high quality of service and moves more data than asynchronous techniques. The system clock on the sender and receiver is made to tick at the same time so they are synchronised with each other. The data can be moved more efficiently under this approach
Asynchronous data transmission tends to be used on lower bandwidth data transfers where the sender and receiver are far apart and their clocks can not easily (efficiently) be synchronised. Asynchronous transfers rely on a handshake between the sender and receiver. This type of transmission was designed to allow data to be moved off the motherboard onto peripheral devices like printers, scanners, keyboards and mouse('s) and the like. All networking is done as an asynchronous manner.