One of the biggest questions in the fitness space is how to gain muscle as quickly and efficiently as possible. And while a calorie surplus is not always necessary for gaining muscle, no matter how you look at it, a calorie surplus is going to be a necessary step for doing it in the most efficient way possible.
If the goal were just to gain muscle as quickly as possible, it would make sense to utilise a large calorie surplus. But this is where efficiency comes in.
A large calorie surplus is likely going to lead to a lot more fat gain and an unfavourable ratio of fat to muscle gain. This then either leads to more time having to be spent dropping body fat down the line, or just decreases how long you can be in a calorie surplus for before having to drop back to maintenance calories. Therefore, too large of a calorie surplus is typically inefficient since it slows down the process of getting to your ideal physique.