Selective forwarding function

The task is to create a single-argument function that forwards all types apart from one (Foo), which it converts (to Bar).

(Let us assume there exists a conversion from Foo to Bar).

Here are two implementations:

template<typename T>
T&& process(T&& t) { 
    return std::forward<T>(t); 
}

Bar process(Foo x) { 
    return Bar{x}; 
}

And...

template <typename T, typename U>
T&& process(U&& u) {
    return std::forward<T>(std::forward<U>(u));
}

template <typename T>
Bar process(Foo x) {
    return Bar{x};
} 

I have it on good authority (here) that the second one is preferable.

However, I can't understand the given explanation.

Could someone explain in detail?

PS In case it is relevant, the context in which the function is being used is given here.