Question: Consider the following C++ code:

```
double someZero = 0;
std::cout << 0 - someZero << '\n';   // prints 0
std::cout << -someZero << std::endl; // prints -0

```

The question arises: what is negative zero good for, and should it be defensively avoided (i.e. use subtraction instead of smacking a minus onto a variable)?

Answer: 
In addition 
Signed Zero Good For :

The zeroes can be considered as a variant of the extended real number line such that 1/−0 = −∞ and 1/+0 = +∞, division by zero is only undefined for ±0/±0.

Negatively signed zero echoes the mathematical analysis concept of approaching 0 from below as a one-sided limit, which may be denoted by x → 0−, x → 0−, or x → ↑0. The notation "−0" may be used informally to denote a small negative number that has been rounded to zero. The concept of negative zero also has some theoretical applications in statistical mechanics and other disciplines
There are only two real use-cases that I can see:

1. You want to show that a value is negative but very very small (perhaps infinitessimal), i.e. too small to represent as a float or double.
2. You are working with math that only allows negatives, but still want to display zero. There are a few cases in physics, complex numbers and number theory where this can be useful.

For the mostpart, it's not useful and should be avoided.

You may also want to take a look at this question: [Is there a negative zero?](https://stackoverflow.com/questions/4199808/is-there-a-negative-zero) and the [IEEE 754 spec](http://en.wikipedia.org/wiki/IEEE_754-2008 "IEEE 754 float spec") for floating point.