No money is actually in the coinbase account. It only stores Bitcoin. If you sell bitcoin, the USD balance will immediate be ACH'ed directly to the bank info you have set up.[1] Otherwise, I guess you won't be able to use the sell feature(?). BTC-e.com is different; you can sell all your coins and have a USD balance[2].
You can create a Coinbase account without banking info. But after you've created it, I'm not sure what good it would be to you. I guess you could just use it to manage your bitcoins and have one place to check. But the real service coinbase provides is transforming BTC to USD and vice-versa. If you're not going to enter your banking info to use that feature, you might as well generate a pub/priv key at bitaddress.org and just make sure you don't lose the private key.
You can create a Coinbase account without banking info. But after you've created it, I'm not sure what good it would be to you. I guess you could just use it to manage your bitcoins and have one place to check. But the real service coinbase provides is transforming BTC to USD and vice-versa. If you're not going to enter your banking info to use that feature, you might as well generate a pub/priv key at bitaddress.org and just make sure you don't lose the private key.
1. http://i.imgur.com/LMowl3F.png
2. http://i.imgur.com/3K1JPgR.png