Surveyors often need to cut lines of sight through some of the nastiest, thickest stuff imaginable, most often without any sort of mechanical assistance. On very rare occasions you can get someone with a Bush Hog or some other tractor-mounted device to assist clearing along fence lines and such, but most often not, for a variety of reasons.
Machetes are next to useless for a lot of what the field crews contend with - so the brush hook (bank blade) becomes your primary tool.