Once it is foamed, then I use a wash pad (or the new Wash Wedge) to clean the paint. The foam cannon just gets a lot of soap onto the paint, making it safer and saving time, since you don't have to keep going to the bucket for more soap.
Truth be told, laying on a full white coat of foam was for the pic. The foam only hangs for a few minutes, so I typically foam three times. The first foaming is the hood, roof and windows, then I use the pad or Wedge and rinse it in a bucket of clean water as needed. Second, I foam and wash the middle sections, basically between the windows and the rockers. The last foam application is on the rockers and bumpers, saving them for last since those areas are the dirtiest.