It is a firmer commitment on behalf of the mortgage company. The credit report is already done, and the terms are subject to the appraisal of the house you intend to purchase. It is easier to negotiate with a home seller, and closing the transaction usually takes a shorter period of time. Pre- approval also makes the home buying process less stressful knowing that you're already approved. A loan officer will respond by a phone call, e-mail, or letter.
All information is held in strict confidence.