Although I don't do as much flyfishing as I did in prior years I've tied a lot of bass flies over the years.
Anyway, the point I was gonna make is that I made a lot of them weedless by tying in a loop of heavy mono that covered the hook point. I didn't seem to have a problem hooking up with bass or northerns with flies tied in this manner so I would have to assume that the hackle wouldn't pose much of a problem unless the hook is very small.
If that's the case I could see where excessive hackle could interfer with hook setting.

 

That's a tough question. My guess would be that over-hackling a dry fly would be bad when working with the smaller flies, as it might distort the profile some. Large flies like hex would surely benefit from more hackle, since it would add to it's buoyancy. The main purpose for hackle is to make the fly float. A propotionate amount of hackle will keep your fly floating better, as well as enhancing the overall profile while in the water. Too much hackle might also cause the barbs to splay out in different directions, resulting in the fly not floating properly in the film. Many times you will hear that tying flies "sparsely" is the way to go. Use your own judgement--put on enough hackle so that your fly will consistantly float, but don't overload it to the point of not being able to tell what kind of fly it is.

HATCHBOMB

 

Hatchbomb pretty much hit the nail on the head, buoyancy is the main purpose followed by balance as a close second. Assuming these flies are imitating naturals and assuming you tie in enough to keep it floating, trout fishing flat water sparser is ALWAYS better. The cleaner profile for the body the better, hence the popularity of parachutes and comparaduns. Hex you need the bushyness so you can be sure they're floating well at night when you can't see them. Even then I tie a few sparser hackled flies for the occasional daylight action. Often times I'll tie my hackled mayflies(e.g. Adams or light cahills) with varied densities of hackle. On faster water I'll use the heavier hackled flies and use the sparser stuff on the flat water. On the attractors such as coachman's and trudes I don't worry much about as all your looking for is a "buggy" looking fly. As far as the length of hackle Vs the hook gap. I usually select hackle just slightly longer than the gap basically enough so that if you set my fly on a table after it was tied it would set level on the table after the give of the hackle tips.

 

fishinlk subscribes to my theory. Fish the more accrurate, sparser imitations in the smooth stuff where they can examine it more. Use the heavier hackled in the rough, faster water where buoyancy is an issue. I catch just enough to keep me subscribing to that theory.

 

What fo you mean by "over hackeled"...

Do you mean too many wraps around the hook shank? I think this is what most of the posts are talking about.

Or do you mean the actual length of each fiber. I think the "classic" ratio is that the hackle fiber should be 1 1/2 times the hook gap. This allows the fly to rest on the water with just the hackle and tail touching.

Has anyone else heard this, or is my ignorance showing again...

 

I was intending to mean too many wraps around the hook, rather than too large of a fiber size.

In thinking about it, larger barb size wouldn't be as bad as too many hackle wraps. My logic is that with too many hackle wraps, it makes tying the head and whip finish a pain. If you use a larger barb hackle and wrap it sparsely you'll be fine.