Because its the gracious and correct thing to do. Why pay for groceries when you can go to a food pantry? Why give a tip to your waiter? Why pay for clothes when you can go to Salvation Army?
If a woman wants to feel slutty or whorish, a bit of your beer money will make her feel very special in the fulfillment of her fantasy. Other may feel offended like that hot receptionist at your office. BUt the whole idea is about that beautiful unfaithful pussy realizing her fantasy.