I used to throw them out, sometimes still do, but I do have several piled up in various drawers. As for being able to finish them.. It's quite common for me, even with my very large wardrobe to get hooked on one scent and just wear the crap out of it until it's gone. 3.4 oz, being worn every day, twice a day if reapplied, sometimes more depending on the longevity/projection, this bottle can be gone in 2 months easily. 3.4 oz is a lot when you switch around and rotate fragrances religiously, hell 1 oz is a lot if you have a huge rotation.. but if you stop and get hooked on something, and you have 100 to begin with, that means you love your fragrances, and you're really gonna wear them. Back on topic though, I usually just save bottles of the ones I like, and sometimes if I get desperate enough, I'll see if i can get a whiff out of the empty bottle.
Lately though, when I get down to the last of the bottle, I'll leave a little bit.. say 2-4 ml or so, then throw the bottle in a drawer.. this way if i ever get the craving to smell it, there will still be some in there.