Yes, there is a difference. Using a ML1100 I needed to do three concatenate (ACN) instructions in order. I tried using parallel branching but it would not compile. Nested the three and it compiled and worked in the proper order.
It would not compile. When I clicked on the error message in the popup tab at the bottom it highlighted the branches. This led me to believe that the branching technique was wrong so I changed to this:
I never changed from nested to parallel and from all the time I spent looking at the program I had convinced myself (incorrectly) that they needed to be nested.