참고 문헌
https://kt.academy/article/ek-mutable-collections
The biggest advantage of using mutable collections instead of immutable collections is that their performance is faster. When we add an element to an immutable collection, we need to create a new collection and add all elements to it. Here is how this is currently implemented in Kotlin stdlib
When we deal with bigger collections, adding multiple elements to another collection can be a costly process. This is why using mutable collections, especially if we often need to add elements, is a performance optimization.
Adding mutable collections to elements is generally faster, but immutable collections give us more control over how they are changed. However, in the local scope we generally do not need this control, so mutable collections should be preferred, especially in util functions, where element insertion might happen many times.
