The only reason I can think of is for situations like the Walleye fishing here this Fall. The Walleyes have been feeding in the dark on Emerald Shiners which are running at the surface. Any weight at all and you are fishing under the fish. Till this Fall I have almost exclusively used Clousers, and therefore had a box stuffed full of them. Imagine my frustration when they were popping all over the surface. I should also tell you that where I fish is very snaggy. The whole town burned to the ground in 1910 and they shoved a lot of the junk into the reiver there. It also has a railroad bridge and when they do work on it and the tracks it seems they just toss the metal they replace over the side. You can loose a bunch of flies in no time there. I started to tie them on #2 Abeerdeen hooks, and bend the eye down with the vice. If you use a tippet of even 10lb test you can get the hook to straighten out enough to come free most of the time. I think most of the ones I loose are wedged in cracks and hung on the eyes. I have no way to prove it, but that's the feeling I get. I have landed a bunch of really big fish on them tied with Abeerdeen hooks, including Pike over 40", and never lost one to a bent out hook. It is a different place you pull on a fish, than on a rock or hunk of steel. The fish is back in the bend and the junk is up on the point. My 'replacement' tying was drastically reduced by going to these hooks. Here is a link to another thread where I talked about the Walleye flies;
The case for tying your own.