Are you going to fish from a boat? Are you going to fish mainly on ponds, big lakes, streams? You might want a beefier rod (and heavier fly line) for big water or other exposed (windy) sites. Are you going to be using micro-jigs? Are you going use bigger jigs, like 1/80 and 1/64 oz.? The bigger, bushier, heavier flies need a heavier line to cast them. Are you an ace caster? Average? Not quite average? The heavier the line, the easier it is to cast big and bulky flies.

Regards,
Ed