Why use float and double instead of real?

[Lars T. Kyllingstad]

Is there ever any reason to use float or double in calculations? I mean, 
when does one *not* want maximum precision? Will code using float or 
double run faster than code using real?

I understand they are needed for I/O and compatibility purposes, so I am 
by no means suggesting they be removed from the language. I am merely 
asking out of curiosity.

-Lars