As a general rule, 90% of the execution time of your program
will be spent in 10% of its code. Profilers are tools that help you
identify the 10% of hot spots that constrain the speed of your
program. This is a good thing for making it faster.
But in the Unix tradition, profilers have a far more important
function. They enable you
to optimize the other 90%!
This is good, and not just because it saves you work. The
valuable effect is that not optimizing that 90%
holds down global complexity and reduces bugs.