I'm trying to understand the factory design pattern.

I don't understand why it's good to have a middleman between the client and the product (object that the client wants).

example with no factory:

$mac = new Mac();

example with a factory:

$appleStore = new AppleStore();
$mac = $appleStore->getProduct('mac');

How does the factory pattern decouple the client from the product?

Could someone give an example of a future code change that will impact on example 1 negative, but positive in example 2 so I understand the importance of decoupling?

Thanks.