It protects you from exchange rate risk. just like a stablecoin does.
Like if you need to hold a part of your paycheck so that you have at least $1,000 at the beginning of next month for rent, regardless if bitcoin sees a selloff before then. So you buy (peg ?) this USD, then at the first of next month when rent is due, you sell (unpeg ?) and you have $1,000 worth of bitcoin to spend at that time. If your landlord wants cash, you still have to sell the BTC or do whatever you normally do to get cash for your bitcoin.