Some examples -
I have a lot of barbed wire fencing around for cattle. Fencelines run through forest and saplings grow through them all the time. When I cut the trees out I'll often use a large knife (what I have on me when I go walking around). Because the wood grows through and around wire, it means occasionally chopping hard into metal (and sometimes stone if it's rocky ground. I've done this with 52100 (which is pretty tough) and gotten a lot of chipping. INFI = no chipping.
When I go four wheel driving in national parks and state forests (e.g. for hiking or hunting), down little-used and sometimes partially overgrown roads, there are a lot of downed trees across the road. If I don't have a chainsaw with me I have to use either an axe or a chopping knife (depending on the size). This means sometimes hitting the ground (rocks, gravel). Tough chopping knife = no chipping.
A few months ago we were spreading grass seed and clover around a freshly under-scrubbed and raked area of regrowth forest using a tractor. The seed spreader operates off a PTO (a shaft attached to the tractor engine that spins it). When we fired it up it caught the cover on the tray of the ute and sucked it in... it wound around the shaft of the seed spreader so tightly (a tractor motor is strong!) it basically turned to rock. It was some kind of mix of shadecloth / rope and some wire. A lot f it was too hard to cut. So we had to put the point of the knife into it and baton the pommel with a rock, and chip it out bit by bit (which also meant bashing the tip into solid steel repeatedly). No damage.
When batoning through knotty hardwood (for kindling for my home fire place) I also want something tough.
Stuff like this needs to be done sometimes and if the only thing you're carrying is a knife, then toughness becomes the biggest factor.
I can't wait for Nathan to make a Bowie grind. 
