Why do clamshell grab bucket and telescopic arms always appear together

Today we will take a look at all kinds of excavators equipped with clamshell grab bucket. Because of the telescopic boom, the clamshell grab bucket are basically bound together by the telescopic boom. In various construction projects that require deep excavation. , Is an excavator equipped with a telescopic boom and a clamshell grab bucket doing the work that used to be done by a machine excavator and a transport vehicle.