Why don't we switch to C like floating pointed arithmetic instead of automatic expansion to reals?

[Walter Bright via Digitalmars-d]

On 8/6/2016 1:06 PM, Ilya Yaroshenko wrote:
> Some applications requires exactly the same results for different architectures
> (probably because business requirement). So this optimization is turned off by
> default in LDC for example.

Let me rephrase the question - how does fusing them alter the result?