Become familiar with the hatch stages where I am fishing and what patterns works best during a particular time of day and month.
Learn to read the water, as to where the different species of trout hold
Since most of the feeding by trout is down under, learn to fish the nymph pattern better
Learn how to use the streamer more effectively in fast water verses slow water
Recognize hot spots and never forget where they are on a particular stream you might be fishing
And last—realize that a guided fishing trip for me is not all about landing a lot of trout, but more of a learning experience—in other words think of the outing as a day spent in an outdoor classroom.
Feel free to list your own advantages