The script interpreter runs as a separate task in the cube as well as any other games.
Good practice in a script is to perform so called co-operative multitasking. That means, after you have done what you needed to, you should use the Sleep() function. If Sleep() is not used, nothing bad will happen - the system will cut out the script for a while and give some time to system tasks.
If the script is not complicated, no one will ever notice that Sleep() isn't called.
If it is important to delay the program or wait for something, like waiting until music playback is over, you should always use delay functions with the built in Sleep() instruction. These are, for example: Sleep(), WaitPlayOver(), WaitMelodyOver().
The following pictures show simplified scheduling and recommended basic programming workflow.