This command does not refer to having lots of empty space on your Day-Timer. It removes compiled programs from memory.
CLEAR PROGRAMFoxPro caches programs to improve execution speed. Normally, it does a good job of noticing when you change a program and dumping the old version in favor of the new. However, under some circumstances, it messes up and runs the old version. That's when CLEAR PROGRAM is called for.