Keeping some PI around
You never know when you might need PI for doing some calculation. Now some people just memorized the digits, but back in high school we learned that 22/7 was pretty close (3.14289 vs 3.14159) and that's pretty easy to remember. In fact, when playing today I remembered it without trying. However, if you need a few more digits, then 355/113 is really close (3.1415929 vs 3.1415927).
Good enough for sheet metal work, that's for sure.