Defaults are quiet decisions made before a particular situation arrives. A good one makes the ordinary path clear without hiding the exit: save the draft, preserve the original, show the result, leave a way to pause.
That is a useful standard for tools and routines alike. A default does not need to predict every case. It only needs to be safe enough to start from, visible enough to question, and easy enough to change when the context asks for something else. The most helpful defaults reduce the small chores while keeping the important choice in view.