Funny story. I used to have a 7'10" no-name medium-action 4 weight that was my favorite rod, and got used 90% of the time. One day, I was casting some monstrosity of a cone head fox-tailed streamer across a deep pool, and my fishing buddy, who's about the best fly fisherman I've ever come across, complimented me on my double-haul, surprised that my wimpy little rod could toss that streamer 60 feet. I hadn't realized that what I was doing was a double-haul until he told me. I find it to be an enormously useful cast, even on the small streams I fish in the Driftless area. Casting up or downstream 40 feet or more is an advantage when the fish are spooky.