Some people argue that even if you have a strict no-shoes policy in your home, you could still spill coffee or red wine on your carpet and cause permanent stains.
This is true. You can still spill red wine or coffee in a shoeless home and cause permanent stains (those of you who are teetotal will say 'Don't drink red wine then.' As it happens, I do not drink wine, just beer and spirits. I do drink black coffee, though).
However, do you want a carpet with stains that is full of dust, dirt and bugs or a carpet which has stains, but is a lot cleaner?
Stains do not cause wear and tear to carpets, though they are messy. The tiny grit particles that your shoes pick up do wear your carpet out.