When is only carrying one tool, it's nice to know it can take abuse - then you decide whether to abuse it or not.

When you can carry multiple tools then you can find one matched to your specific need. If I have an axe then I don't need my knife to do so much chopping - if I have a prybar then I won't need to use my knife to prise anything open.

Knives are - usually - suboptimal tools with a lot of versatility. Specialist tools (skinners, machetes, scissors, chisels, saws etc) will do a better job but add weight/bulk.

YMMV