I have one that I've recently had repaired and is waiting to be hung. I think these were used for general rough hewing. Most were double bevelled - though single bevelled ones were used, too.
I think the reasoning behind this design is that with this one axe a fellow could rough hew a large timber expeditiously. Think - notch, juggle and smooth with one axe. In a pinch you could even fell with it. If you were operating a sailing vessel 250 years ago your mast was your engine. Being able to fabricate a new engine on the spot was a critical ability.
http://mudpondhewing.blogspot.com/2012/07/origins-of-north-american-pattern.html
I can't help but notice the similarity to Kent pattern axes.