Steve Voigt
I don't mind elaborating, but there is not that much more to say…still, here are few random thoughts.
The oldest written source I know of on planemaking, Armour's "Practical Planemaking" (from around 1900), mentions using a gouge to chop the initial mortise. The reason is that a firmer gouge is to a chisel what a jack plane is to a try plane or jointer. The analogy is not perfect because gouges have many other uses, but many people overlook the gouge's ability to hog off material. It's not so much that it can take a bigger cut; it's that it can take a similar cut with much less effort.
For roughing, you want a very stout gouge, not a delicate carver's gouge. You can use either incannel or out, but as I said before, incannel is faster. There are tons of old American socket gouges that will work.