The carbide doesn't wear out, it pushes up through the plastic holder and into the tube. Sometimes you can hear it rattling around in there. Once the tip is no longer sticking out the end of the plastic holder, you can't trust the pole to hold onto rock anymore. It will slip - which is very annoying.
All the scratches on the rocks, be it from poles or crampons helps reassure your still on the trail. Ever notice in the early spring the only place which is green is along the side of the trail? Poking holes in the soil along the edges keeps it loose and aerated, promoting growth.
The small baskets do help keep the pole going too far into the ground or into a hole. Still gets snagged 3-4 times a day though.