From man page: fio is a tool that will spawn a number of threads or processes doing a particular type of I/O action as specified by the user. The typical use of fio is to write a job file matching the I/O load one wants to simulate.
This example only show how to use fio to make reproduceable test on a file system. For me it’s been useful to catch changes in I/O throughput before and after a system has gone into production. Buy running the same tests on all systems the numbers are comparable.