It can be useful in case of having a list, you can make two Add. One gets one item and the other one gets an array for bulk operation. Yes I can make Add and AddMany for example but it is more clear to have them under the same name.
Or for another example, having Sum function that one gets two items and another one gets two arrays.
This is not just limited to arrays, maybe you like to have the function for pointers too.
All I explained, can be made with different names, but it is more consistent to have them with the same name, eg add, sum.