Catch

Putting aside the fact that using magical circles in the first place was difficult, they were quite effective. But their power did match the difficulty of mastery. It was to the point that they wouldn't teach it to any of the first-years, even if they were in Class S. And even though they did teach it in further years, few people actually were able to utilize them in the first place.

The main function was using mana not to actually cast the spell, but to make something that would rapidly accelerate the actual spell casting itself. The best way I could explain would be to compare normal spell casting with molding something using your hands. The idea of a magical circle would be a container in the proper shape of the mold along with a catalyst that makes it easier to mold in the first place.

It was effective enough to make spell casting that would normally take a minute simply take a few seconds.