Start using your lens hood all the time. The primary issue with scratches on the front element, as noted above, is lens flare and loss of contrast. This mostly happens when you have a strong light source in the image or just outside. The hood will help prevent any strong side-lighting from catching the scratch and giving you an odd light artifact in your final image.
Back in the bad old days of small-town newspaper photography, we never used lens caps, we cleaned our lenses with our shirt tails, and my front elements had many small scratches in the coating. We just used a higher contrast grade of paper for printing. No big deal.
A scratch in the rear element is more problematic.