Both are necessary for the wilderness, especially if you don't carry an axe Easy Cellar or tomahawk. The definition of a large knife varies, but most people have it in the 7-9" and up range.Big knives can be used for the big jobs that a Fallkniven F1 or similar size knife just can't do with any facility, but can still handle most of the smaller, finer jobs that the small knives do.
They can be used for any kind of heavy work, such as chopping, batonning, clearing branches, and such. Batonning (splitting small to medium chunks of wood by driving the knife through the wood with a wooden baton) is made easy by a longer blade, especially if the grind is suitable.A longer, heavier knife makes chopping a breeze. Sure, it may not be as easy as chopping with an axe, but a knife is a lot easier to carry!
An accomplished worker can do most all of the small jobs as well. A Busse may not clean a fish as well as a Buck Vanguard, but it will still do the job and works immensely better for shelter building and procuring firewood. The best option is to just carry a folder or a small fixed blade along with a chopper.Big knives can be found in any configuration desired.