Drawbacks of exceptions being globally allocated

[Tejas via Digitalmars-d-learn]

What is the drawback of the following "simple" ```@nogc``` 
exception creation technique?

```d
import std;
void main()@nogc
{
    try{
        __gshared a = new Exception("help");
        scope b = a;
        throw b;
    }
    catch(Exception e){
        printf("caught");
    }
}
```