I saw a thread on another forum about the weight of flies, and the question of how much flies weigh was never actually answered. From a practical standpoint, I imagine it doesn't matter so much with dries, as the weight is only one factor in keeping them afloat. As for nymphs and wets, rate of sink and the position in the water column you wish them to hold would be affected. .....A factor of significant importance to euro nymphers and centerpin drifters. To the average flyfisher/flycaster I'm not sure if the very small difference glues and cements make would be of much concern. Larger, heavier, flies, such as big stonefly nymphs, clousers, and certain beadhead and dumbell jobs do affect 'feel' and loading when flycasting. Just my thoughts on the matter..