As a profesional you build up a set of tools which you use to face the chalenges of your job. In the old days your library was one such resource, and if stuck you would look up the information you needed.
The role of your PLE is similar, except now you are adding people into the equation. If we phrase the PLE as a PLN it makes it much clearer that this is a network of like minded individuals, facets of whose activities overlap, and who can aid each other like fellow travelers where this ocurs. For me the primary purpose of my PLE/PLN is to leverage on the experience of others and avoid re-inventing the wheel.