I think we all agree that the environment and the surroundings determine the need for, and the type of cutting instrument that is optimum. I am kind of dismissive of the crying need for a Rambo knife on land, but let's change the setting.

If you are out on the water, either real water like the Santa Barbara Channel or those glorified teacups they call lakes in Minnesota,:) you definitely need a knife, probably a fixed blade. Although it doesn't need to be long, it does need to be sharp. On a vessel there are too many lines, and too many chances for critical entanglement (in propellers and things like that). If you are going underwater, a knife that is in easy reach is essential and absolutely necessary. This is one environment where a Rambo style shines (unless you let it get rusty, but that would never happen, would it?).