I carry a Leatherman Supertool on my belt (left side) and a Spyderco Police model clipped inside my right pocket. Others have pointed out redundancy, ruggedness, and the advantages of one-handed operation. These are all important to me. In addition, the Spyderco serves as a backup weapon, due to its size, blade design, and ability to get into action quickly. Being an LEO, it is important to me to have the tools on the multitool, but also important to have a knife that can also be used when another weapon might be unjustified or unavailable.

If I were out in the woods, I would carry more than one knife because they are designed for different tasks. It would be difficult to clean a fish with a machette, or clear undergrowth with a multitool.

It seems to come down to what it always comes down to here: What you normally do, where you normally do it, what you believe are realistic risks that you are preparing for, and any legal concerns.