The difference is this.

1. IF you load a flight plan into FSX using the FS Flight Planner, you don't need INS or DNS. But...If you fly an INS or DNS plan DON'T load one using the FS Flight Planner. Here is how I do it:

If I'm flying a DNS plan. I have a peace of paper that gives me the heading and distance between waypoints, that I have to set for each leg of my flight (can get tricky when waypoints are close together).

If I'm flying an INS plan. There are two ways to do it. One is with the Plan Converter witch I just load into the INS at the correct times (pretty easy). The other way is that I have a piece of paper with the waypoint co-ordinates written down, that I need to enter as the INS allows them  to be entered and this can also be tricky when waypoints are close together.

When flying a DNS or INS flight plan in the 707, I do not load a flight plan into FSX using the FS Flight Planner. It has been a long time since I flew an FS Flight plan in the 707. There is no harm in doing it in any of those three methods that you prefer. Whichever way makes you happy is the way you do it.

Mark