What's the point of NSAssert, actually?
I have to ask this, because: The only thing I recognize is, that if the assertion fails, the app crashes. Is that the reason why to use NSAssert? Or what else is the benefit of it? And is it right to put an NSAssert just above any assumption I make in code, like a function that should never receive a -1 as param but may a -0.9 or -1.1?
Answer
Assert is to make sure a value is what its supposed to be. If an assertion fails that means something went wrong and so the app quits. One reason to use assert would be if you have some function that will not behave or will create very bad side effects if one of the parameters passed to it is not exactly some value (or a range of values) you can put an assert to make sure that value is what you expect it to be, and if it's not then something is really wrong, and so the app quits. Assert can be very useful for debugging/unit testing, and also when you provide frameworks to stop the users from doing "evil" things.