This trope is one of the primary advantages some media types have over others. Anime and manga, literature, and webcomics usually decide how the magic system works before they even start, and move on from there. Live action are usually much worse about this, and end up fumbling and falling into New Powers as the Plot Demands more.
It's been said that as long as magic causes problems for the main characters, it can be free-form and arbitrary; but once it starts being used to solve the main characters' problems, it needs to be given strict limits. Traditional fiction almost inevitably had magic causing trouble but not resolving it — except for fairy tales, in which magical gifts tend to be symbolic representations of real-world skills.
