Also, keep in mind that you can correct anything with an AIO and a single pad, but the number of passes needed to do so may just be too time consuming. When I do a production one step detail, I explain to the customer that typically it will remove up to 75% of the light defects in the paint and will lighten or hide many of the deeper inperfections in the paint. Long, deep scratches would require a separate compounding or wetsanding step to remove them before the use of an AIO.
Of course, I am only spending about 2.5-3 hours polishing out a vehicle on a one step polish (one section will involve about 3 passes over the same area), so if you are going to be spending 8 hours polishing out a vehicle with a one step polish, you will get much better results, but your time would be better spent using a more aggressive polish/pad first and then following up with an AIO or a finishing polish.