Sometimes i think "we" -- meaning me, many of you, and especially folks who work in shops and sell reels/lines, tend to stuff too much backing on reels, even to the point of making the fly line crowded on the reel if you reel in the line a bit sloppily. I think we let the amount of backing become too big an issue sometimes in determining reel size to buy. How many fish do you catch that get into the backing anyway? How many way into the backing? All the way to the reel? Moment of candor here: I hook and land some 20+" fish every year with 4-5-6 wt rods/reels/lines, but about half the time i see my backing i have foul hooked a fish who jumped in the current and took off for the next county. For bigger reels used in salt or for salmon/steelhead, the issues are probably different--i dont really do that. For folks fishing garden variety trout rods and reels it is often worthwhile to get the next size down in reel, and live with less backing--which you are never gonna use anyway. I have one reel that i will use where all the fish are going to be 15" or less and i just tied on a few yards of backing to keep from tying the 90' fly line directly to the reel.