Given the choice of two applicants, one who simply repeated his/her bad courses, and one who took a post-bac [and did well], I'd pick the latter candidate.
These programs show us that someone really can or can't handle the difficult load of medical school.
Benefits of the former are they're faster to get through, and show that your poor performance was due to poor choices, bad luck, outside-life problems, and that the poor course performance were just a fluke.
Downside to post-bac: 1-2 more years of classwork; more $ than merely repeating courses. One of the harsher benefits is that they show you that you're not cut out for med school.