That's a good question, yet people do it. You're sitting around waiting for a week for your money, you see a game you want to bet on, and instead of depositing more money you bet from your existing balance. This happened to me a few years ago - I was waiting for an $8000 payout, doing the usual BS with faxing your credit card, ID, etc. that non top-tier books make you do to get your money (stalling tactics, I've heard them called). Then Villanova had that phone-card business where they had to suspend half of their players, so I threw $1000 on Pitt - 10 against an undermanned Villanova team starting two walk-on players, but Villanova played the four corners offense the whole game and almost ended up winning. Long story short, I made sure to get my payout squared away immediately, but I could see someone in that situation trying to chase their loss and squandering a lot of the money that they were already waiting to be paid. That makes me think that the number one reason for the slow-pay tactic is that they hope it turns into a no-pay, because you act like an idiot and lose the money you're waiting to receive.