You ask a very interesting question.
There are debates on here (and gripes about medical professionals!) about what constitutes "insufficient" and "excessive" testing.
At a minimum, I suggest testing first thing in the morning, and last thing at night. Those of us who are on insulin and have "twitchy" blood sugar numbers also test before and after meals -- even when we feel like it.
One gathers data to look for trends.
"I wonder what a thirty-minute walk would do." Check before and after.
"I wonder what a bowl of oatmeal would do." Check before and after.
"I wonder what getting angry because I listed to Rush Limbaugh would do." Check before and after. (Yes, listening to Rush Limbaugh angers me enough to cause a noticeable blood sugar spike.)
If your A1c is running at 5.4% without insulin, and you never go above 150, you probably needn't test much.
If you make no insulin of your own, you recently had an A1c of 10%, and you find that your blood sugar varies by 100 mg/dL per day, you'd better make good friends with your meter.
