Horizontal dropouts are the appendix of bicycles. Adjustable screws are almost always set and forget. There used to be a reason for them, perhaps, and they tend to go bad on many frames. I'm always shocked when a frame comes into the Atelier without bent or frozen adjuster screws.
One of the benefits sometimes stated for horizontal dropouts is that one can vary the effective chainstay length between rides. Does anybody actually do this?
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If someone tells you that you have enough bicycles and you don't need any more, stop talking to them. You don't need that kind of negativity in your life.