Otherwise, you can leave tens of thousands of dollars of equity on the table. In the past, MLS systems were localized, though no less valuable. The more buyers vying for your home the more likely you'll get more than you are asking, especially in a tight market. Agents price properties using comparable data. Very few buyers will offer more than that asking without direct competition.
Time is, after all, money.
Half a commission coming in more often can make exclusivity a cash cow. The draw for the seller is exclusive agent who also represents the buyer. Of course, this all raises the dual agency question. Question the rationale of the agent. Get answers to your satisfaction.