Edging is a climbing technique that involves using the side edge of the foot rather than the flat, toes or heel. This technique is used where the foot hold is very small and requires precision. Edging is a skill that takes a while to learn correctly as it is often quite un-nerving initially when trusting your foot on a small thin edge.
Certain rock boots are better at edging than others and some with soft sticky rubber (which is great for smearing) can “walk” or slide off very small edges easier than those with a harder sole. As with everything the trade off is that a hard sole will not be as good at smearing as a soft one. What is worth mentioning though is that you will be surprised at what your rock boots, regardless of the type of sole will be able to stand on. Practice edging as it is a valuable skill.