Allocating Script Memory

Well, reading the stickied FAQ I see that setting script memory to 0 is an option. In truth, I've been doing this for some time now. My question simply put is....if setting to 0 is valid, why have the capability to set memory at all? Is there an advantage to setting this value? Maybe more efficient garbage collection?

*If* it is advantageous to set a value for script memory, two other points come to mind. First, is there a way to determine the optimum value for this number? And second. often computers work best with numbers that are powers of 2, and better still with units of 8. For instance, the default value for script memory is 48, 6x8. Is it best to stick with this scheme.

Moot point if 0 presents no penalties. Thanks in advance for any input.