It’s normally the case that some devices transfer the output either in a bursty or a sequential manner and also during input entry. If we take the example of keyboards, all the data entered is stored in a buffer and given at a time or one character at a time.
In case of networking there may be several requests to access the same resource and all these are queued in a buffer and serviced in the order they are received
Hence to avoid the input/output units from getting overloaded with requests, we use multibyte buffers.