skinnykid02
ArboristSite Operative
as slinger said its to make the butt hit first. usually use it when falling in steep ground or uphill. helps the tree settle.
here in b.c. we call it a swanson undercut, and you can do it two ways (as you said): a humbolt with a snipe, or a very "open" humbolt (1:1 depth to opening). does the same thing, but doing the humbolt with the snipe takes less cutting.
thanks