Let's say you are busted for the check charges. You can't make bond and serve four months in jail before you are sentenced. The judge sentences you to a year in jail but you only have to do eight months, because you get four months TIME SERVED. Credit for time served already.
If you are bonded on a charge, your time served clock stops. In other words once you are sentenced. You do the full year.
The bondsman that bonded her on the "tiny" charges knew she wasn't getting out on the 500,000 grand charge. He just wanted to make sure once she is sentenced, she gets the most possible time in jail. So, when she is sentenced for the tiny charges, she won't get any time served for those charges.
It's cheap advertising and a way of saying..."yeah, we don't like you either Casey Anthony."