When do we need to use float.PositiveInfinity and float.NegativeInfinity?

Question

When do we need to use the Infinity values, kindly add a real-world sample if available.

Answer 1

For example, negative infinity is a natural maximum value of an empty list. With this, you have: max(l1 + l2) = max(max(l1), max(l2)), where l1 and l2 are arbitrary lists, possibly empty.

A real-world application of this principle:

float Max(IEnumerable<float> list)
{
    // invariant: max contains maximum over the part of the list
    // considered so far
    float max = float.NegativeInfinity;
    foreach (float v in list)
        if (v > max)
            max = v;
    return max;
}