High Casual is essentially advanced, [@Ace of Hearts]. Such topics are put in the Casual section to attract the casual RPers. It grew forth because advanced was once (long ago) plagued with a considerable number of elitist jerks. The people who use the label tend to either want to attract different players than advanced does, or not quite feel up to running an advanced RP. Many people feel advanced has much stricter requirements than it actually holds.

In essence: Its advanced without the label.