The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.
With those bigger flies I find it easier to cast if you slow everything down. When I first started out it seemed to take a year before the loop would open and the rod load. If you try to cast too fast you will lose all momentum and end up with a mess at your feet. Over-lining helps keep that energy through the cast, and the cast tends not to collapse as much.