Patent professionals recommend classification searching as the best way to conduct a comprehensive patent search. Classification helps bring together similar devices and concepts, even when different terms have been used to describe them.
We may think that we know all of the variant terms used but when a technology is new, the language isn't set. For example, before personal computers a mouse was nothing more than a rodent. The inventor of the first "Computer Input and Display Control" would not have found related devices by searching the keyword "mouse."