in the days before biomass was financially viable in remote parts of northern maine (and other areas) once the money wood was cut off the left overs needed dealt with before replanting could commence. the tree crusher would take care of brush, saplings, malformed trees that werent worth harvesting, etc.
they dont have much use anymore. clear cutting doesnt happen as much as it did then. but they are still used from time to time. ive seen pictures of one in northern maine or new brunswick. the operator forgot where he parked his pickup. he had to walk home.