lots of good advice here! i tend to grab a certain wt. rod for a few reasons...
1. how big of a fly do i want to throw?
2. what type of water and structure will i be fishing?
3. will wind effect my casting?
4. are there good chances of hooking a bruiser?
and thats basically the order i go by. i tend to fish 6-8wts. alot for bass. if i just want to target a variety of fish i grab a 9' 5 or 6wt. now i have 2 and 4 wt. that i take to small spring streams. they are a blast and i have actually caught a big LM on the 4wt....BUT, it wasnt fun to me. sure the fish fought and it took a bit of time to land. only way i can describe it, its like deer hunting with a 22lr, sure it can and people have killed deer with such a light round but doesnt seem right
( on top of being illegal). just ask yourself the 4 questions above and that will help alot. some days though its just fun throwing big bugs and watching the action.