pxia

When the gain is smaller than the cost of hiring people to do the claim.

It's just an example... Another example would be you want to iterate your array in reverse. The normal `for (uint i=size-1; i >= 0; i--)` won't work.

Because you want to represent errors. For example a find() function that returns the index of some element: you want to return -1 when the element doesn't exist.