why pass by universal reference?

[JUANDENT]

I understand by universal reference the argument passing following this pattern:

template<typename T>
void f(T&& t)

as in

template< class ExecutionPolicy, class RandomIt >
void sort( ExecutionPolicy&& policy,
           RandomIt first, RandomIt last );

Why do we need to do this? why not pass by "normal" reference?

[Peter87]

Universal references are useful when you want to move the argument if it is an rvalue and copy it if it is a "normal" lvalue reference. To accomplish this, std::forward is often used. To do the same without forwarding reference would require two separate overloads.