Over the last few years I have begun to experiment fishing with some longer fly rods. I recently picked up one of the new Hardy Marksman River 10' 4weight rods. I matched this stick with the new SA Textured Nymph Line to make one of the best nymphing setups that I have ever fished. The rod has been able to easily handle dry dropper, deep nymph rigs, and can throw a size 2o Griffith's Gnat to selective fish.
There are a couple advantages that the longer rods have to offer; better line control, added reach, and a more positive hook set. A lot of people think that longer rods are meant to be used for European fishing, but this is not case. Traditional anglers will fish these rods with more success than their 9' counterparts.
The biggest challenge that a fisherman faces, is keeping your line off the water in an effort to obtain a drag free drift. These long rods allow you to keep your distance from the target while maintaining total line control during the drift. I have really noticed the advantages of the longer rod while fishing anything from Boulder Creek to floating the Colorado.
The other big advantage is, mending. Mending is a very key for fisherman, especially if you are vertically challenged like me. I bought my first long rod in 2000, for fishing the North Platte River in Wyoming and it has allowed me to fish some of those deeper runs more effectively and in turn I got more fish in my net.
Last summer we floated the Colorado for a few days. I used that rod the entire time and fell in love with it. I found that I could do anything with it and will remain a key rod in my quiver.