In theory, every additional binary configuration item doubles your state space, because you have all the old state space, but now both with that value on and of

In theory, every additional binary configuration item doubles your state space, because you have all the old state space, but now both with that value on and off. It is tempting to say that in practice the result is less than this, but in practice, it isn't. Adding a binary option may seem not to double the state space because it only modifies a small portion of the original space. e.g., imagine an option that the user sets to force all emails to be in ALL CAPS. Strong abstractions can mostly contain that state space increase in a principled manner to just that email code, for instance. But if you've been doing this for ten+ years, you've almost certainly encountered the moral equivalent three other supposedly equally-well contained things interacting to produce a bug. Maybe if the user set this setting to true, and was using your UI in Armenian, and all the other settings on the page are in their longest possible form in Armenian, and your UI guy used a fixed-size frame ever so slightly incorrectly, your setting disappeared off the UI entirely, just to draw one example out, even though you had a "proof" that this setting couldn't affect anything but the email code. Any number of other ways this could go wrong. None of our tools are good enough to fully contain the exponential state space explosion exponentially correctly, and it will sooner or later push through your best efforts to contain it. One of the best ways to prevent this is just not to feed the exponential monster.