Every Fly fisherman should have this at home or in his vest. I clean my lines about every third trip out. It makes a huge difference to the floating capability of your line and to the ease of that line sliding through your guides on the rod. Downstream nymphing is so much easier when the line is clean and you can throw small loops in behind your indicator as it drifts down. Mending becomes easier as the line sits on top of the water not in it, it lifts off the water nicely. It is also reassuring that by cleaning your line, you are increasing its life in use. Gehrkes Fly line Cleaner is a well renowned product that is priced fairly.