The longer I fly fish the more I feel that the mend is as important as the cast....maybe more so. The mend makes the difference in catching a fish on the drift and just fishing. While watching my clients fish, I notice that one will be getting more strikes fishing the same water. This usually is because the one getting strikes is mending more frequently and better than the other.
While mending your line, try making a haul on the line (pulling the line with your stripping hand) as you roll the tip of your rod. This picks up the line on the water and makes the mend travel all the way to the indicator or fly. This makes your fly drift the same speed as the current and makes a drag free drift. Usually made upstream, the mend relieves the drag on the fly line and lets the fly be the first thing going downstream. The trout is seeing the current bring its food at the same speed each time. If your fly is presented in the same natural way it will be better received by the fish. Also, each time the mend is made to correct the drift, it causes the fly to start toward the surface in an emerging fashion. I think that this triggers a lot of strikes.
All this being said, I still appreciate a beautiful fly cast. A perfect loop and presentation is an art in itself. A must in dry fly fishing, but since I mostly nymph fish below the surface, the mend is a very important part of the process. The next time you’re making a drift under an indicator, remember the mend and you'll catch more fish.