If dr orders a ct scan of abd/pelvic w/contrast an without, i can see it being done with contrast but what's the purpose of having it also without?

Several reasons: Most of the time, IV contrast is all you need for ct a/p. In some cases, it may be necessary to do both (and sometimes delayed images, too) to fully characterize something (e.g., some adrenal nodules, certain kidney or liver problems). There is added radiation each time you scan, so it is worth asking whether it is necessary for your problem. That said, it is common to do multiple phases.