Well when you really go to think about this, it's really not going to be that hard to simply go to the Coinbase website and do all of this. If you're already buying and want to do it, I'd rather have the satisfaction and sense of security of going on the real site to at least feel a little better about putting my money into an exchange which is ridden with support backlog and issues.
Seems more or less like a waste of time, the only real usage I can see for this is in a time of insane volatility where someone is going to want to get in and out of Bitcoin to make trades. Though this isn't going to make sense as using normal coin-base (not gdax) is going to be RIDDEN with fees. It's a good idea, though it's not really practical in the least for normal usage.