Whats the significance of return by reference?

Question

In C++,

function() = 10;

works if the function returns a variable by reference.

What are the use cases of it?

Answer 1

Getters/setters for instance

class C
{
    int some_param_;
public:
    int& param() { return some_param_; }
    int const& param() const { return some_param_; }
};

but here you should go with some_param being a public int. Containers provide functions that return by reference, eg. vector::operator[] so that you can write v[k] = x.