Why does C++ allow to use a variable in its own initialization?

Question

The following C++ snippet will compile using G++ 4.8.4:

double x = std::abs(x);

It will generate a warning, though:

warning: variable 'x' is uninitialized when used within its own initialization [-Wuninitialized]

Why is that even allowed? Is there any use for such a construct? Or is it compiler-dependent?