A profiler divides the program into small chunks (lines or subroutines)
It reports the time taken by each chunk
It tells you which chunks contribute the most run time
Why is this important?
Suppose you have a program that needs to run as fast as possible
You say "Aha! The keyword search function is too slow. I will speed it up."
You get out the benchmarker and get to work
You research more efficient algorithms
You try many different keyword search strategies