All depends on your type, your regime and your body.
4 times daily is the minimum for the DAFNE regime. I have a history of sleeping through hypos, so if I wake in the night I always test. If I don't wake spontaneously, I set an alarm to test at night at least once a week. I often test after meals or between meals to keep an eye on things because my doses need adjusting frequently. I don't drive - if I did, that'd be an extra test each time before driving. Overall most days its 5 or 6 but often more.
If you have very stable bs, have good hypo awareness day and night, rarely get ill and always eat the same things, fewer tests would be fine. But if you drive, have frequent hypos or viruses, doubt your hypo awareness, or do a very active or unpredictable job it would be irresponsible not to test several times a day.
Even 1 test per day is wasteful if you don't act on the results.