Matching the appropriate line to your rod for a particular application in conjunction with your casting stroke can make or break a fishing situation...period. 

Weight Forward | Aggressive - Short/Abrupt Front Taper - Huge Flies - Sink Tips/Poly Leaders - Heavy Nymph Rigs - Tip Flex Rods
Weight Forward | All Purpose - Average Front Taper - Big Dry Flies - Nymphs - Small Streamers - All Rods
Weight Forward | Traditional - Long/Gradual Front Taper - Dry Flies - Delicate Presentation - Full Flex Rods
Double Taper | Dry Flies - Soft Hackles - Short Distance Presentation - Full Flex Rods
Shooting Line | Aggressive - Short Head Length - Short/Abrupt Front Taper - Distance - Sink Tips/Poly Leaders - Huge Flies - Tip Flex Rods