Gaza, if you start in Africa, you can't take advantage of that rule unless you open jaw to another African destination. The rule exists because for those who want to go to Lagos or Accra, they have no choice but to connect through London, but you also lose all of your African segments. Hope that makes sense. I only wish that they allowed the same thing for Mauritius, which is effectively barred from a OWE without an open jaw. Here are two different simple itineraries where the rule can be used, both starting in Sydney.
SYD-LAX-LON-ACC-LON-SYD (from, to Ghana)
SYD-LAX-LON-ACC//JNB-LON-SYD (via Ghana)