Want to know what flow is play ST and or SM you will have it right in your face. To me a big part of it is the layout providing potential to backhand a wide variety of shots so you can be going towards an objective with either flipper and not have to stop the ball or hit a meaningless shot to get it to a different flipper. It also has to do with speed IMO. Once you string a few shots together and you are in the flow the ball gains momentum and the ball is just flying around the field. Ramp areas and how they return can also have a big impact on how well a pins layout flows. If you have a bunch of upkickers, scoops, and stuff stopping the ball or only one ramp entrance with multiple upper/lower playfields then you are likely playing a pin with very little flow.