Nothing dramatic.

Create two frames. Create a subapp in Frame 1 and use Frame 2 as the frame to display in the subapp. Now go to Frame 2 and resize it. Back in Frame 1 the subapp still has the old size. Even when saving and reloading the subapp stays the old size. You have to rechoose the Frame 2 as the frame to display to resize the subapp to the size of the Frame 2.

This doesn't influence the running app. But it is a bit inconvenient when playing around what size of the subapp fits best