I like to sew my binding on the front and then flip it to the back because I like the way it looks. The machine stitched look on the front (in my opinion) looks more consistent/smoother. When i flip the binding to the back and sew it down, if i don't get the binding exactly straight, it's not noticed as much as if it were on the front. If when i'm sewing the binding down (i do it by hand) and pull my thread too tight, it's on the back and not as noticed.
As everyone as said - it's not "wrong", it's just one way.