For example : You can borrow bitUSD with BTS. BTS is your collaterized promise to pay back the loan you made. With your fresh BitUSD you can buy BTC and transfer BTC to your wallet if you want.
If you want to cashout those BTC : localbitcoin, coinbase, kraken or any other exchange.

I can advice you Blocktrades.com if you want to convert and transfert bitUSD to your BTC wallet easily.