Why overload is done?

#1

why did we overload the operator function? what benefit does it provide?

#2

it is important and used to overload inbuilt functions according to our requirement
for ex
it is used in compare function of priority_queue

priority_queue<node,vector<node>,nodeCompare > pq;
class nodeCompare
{
public:

bool operator()(node a, node b)
{
    if(a.second==b.second)
    {
        return a.first<b.first; 
    }
        return a.second<b.second;
}

};