A boom arm carries the hose and power cable overhead, from the extractor to the tool, instead of letting them lie across the work. That sounds cosmetic and isn't: a hose dragging over a workpiece catches on corners, pulls the tool off line, and on a finished surface marks it. Overhead, the weight is off your wrist and the cut goes where you point it. Tool holders mount alongside so the machine has somewhere to sit between cuts.
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