For conventional layout aircraft, with a suitably sized tail, stable mostly means nose-heavy. Which implies constant negative lift on the tail, and correspondin

For conventional layout aircraft, with a suitably sized tail, stable mostly means nose-heavy. Which implies constant negative lift on the tail, and corresponding excess positive lift on the wings. Which means additional induced drag. All of which adds up to an efficiency and performance penalty. And if the tail controls aren't suitably sized, then the pilots won't have enough control authority to move of of the very stable ballistic arc the plane wants to travel on.