In the process of looking at the source code, I saw that some methods used

enumerateObjectsUsingBlock:^(id _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop);

Then I did some operations in this method. Add the value to the array. What is the benefit of writing this way? What is its specific effect? ​​What is the difference between it and the for loop and the for in loop?