BLA has a rule that every app must pass before it becomes a project: would someone use this as the main app for that function? Not an app the person has installed and forgets. The app they open when they need that thing. The question seems simple. It is eliminatory.
What makes the rule interesting is not what it rejects. It is what it does with what does not pass on the first try. An ordinary rule would work like a door: passed, comes in; did not pass, stays out. The rule of BLA works differently. When an idea does not pass, it does not go to the trash. It goes back to the drawing board.
Take the example of a flashlight. A generic flashlight app does not pass the rule. Nobody picks a generic flashlight app as their main flashlight app, because the system of the phone itself already does that. The idea, the way it arrived, is rejected. In a door logic, it ends here.
But the rule of BLA asks the next thing: what would need to be true for this idea to pass? And then the idea is rewritten. A flashlight with no ads, no login, no data collection. With presets thought out for real situations. With a real international Morse code SOS. With a widget on the lock screen. That flashlight passes, because now there are people for whom it is, yes, the main flashlight.
The idea did not change. The function is still to light. What changed was the form: the set of decisions around the function that turn an obvious utility into a product someone chooses on purpose. The rule did not kill the idea of the flashlight. It redrew the app until the flashlight had a reason to exist.
This holds for the whole line. No BLA app is the first version of the idea that originated it. All of them went through this process of being rewritten against the rule, losing what was generic and gaining what makes them choosable. What reaches the App Store is the version that passed, not the version that was dreamed up.
There is an editorial advantage in this method. When you discard ideas, you end up with few ideas and a lot of fear of being wrong. When you rewrite ideas against a rule, you end up with stronger ideas and a clear criterion of what makes them strong. The rule is not a filter of pessimism. It is a design tool.
That is why the question about using the app as the main one is not asked once, at the start. It is asked all the time, during the project, pushing the app to improve until the answer is an honest yes. The rule is not there to block. It is there to pull upward.