Explain Marketing channels and intermediaries channel structures for Apple products

1. Why are marketing channels and intermediaries necessary? With companies selling directly to customers over the internet in increasing numbers, is this always a good thing? Why do channel arrangements sometimes need to be modified over time?

2. Apple stores sell directly to customers, but you can also purchase Apple products through a number of different retailers. Why do you think Apple has chosen both a zero level channel structure and a multi-level channel structure? What marketing benefits does Apple get through having a brick and mortar store?