Why do some T.init evaluate to true while others to false?

[ag0aep6g via Digitalmars-d-learn]

On 05/26/2016 04:03 PM, ArturG wrote:
> for example:
>
> if(any floatingpoint.init) will be true
> if(any char.init) also true
> if("") also true
>
> while others are false e.g.
>
> string s;
> if(s) will be false
> all others are also false or did i miss any?

What does it matter?