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: 
From Wikipedia:

> 
> It is claimed that the inclusion of signed zero in IEEE 754 makes it much easier to achieve numerical accuracy in some critical problems[1], in particular when computing with complex elementary functions[2].
> 
> 
> 

The first reference is "Branch Cuts for Complex Elementary Functions or Much Ado About Nothing's Sign Bit" by W. Kahan, that is available for download [here](https://people.freebsd.org/~das/kahan86branch.pdf).

One example from that paper is `1/(+0)` vs `1/(-0)`. Here, the sign of zero makes a huge difference, since the first expression equals `+inf` and the second, `-inf`.
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.