In numerical analysis, cancellation is a bad thing. When small floating point quantities are added to large floating point quantities, large errors can result. This fact is fundamental to numerical analysis.

An example, using the MATLAB notation:
>> x = pi;
>> y = 6.022e23;
>> x = x+y -y

x =

It's things like this that make it very difficult to write high quality general numerical libraries. For this reason the well-tested NETLIB libraries are still quite used, despite being written in fortran.