What's the point of testing blood sugar each day when it's likely my sugar level fluctuates all day? what do i do if i test high or low at any moment

Depends: The numbers help your doctor to determine if a change in your regimen is needed. If you are on oral medications, the numbers help the doc determine if a different or additional pill is needed to control the numbers. If you are on insulin, it's very important to check bs regularly so that the dose of Insulin can be adjusted accordingly.

Range control: The average glucose control is important as well, and is tested by the hemoglobin A1c level. But at any moment the body should keep the glucose level within a tight range, which is why it should be tested at multiple times in the day. If diabetic, the Insulin dose over the day should be adjusted to maintain control within the range.

Goal range: It's true it's pointless to test daily if the blood sugar numbers (data) is not being used to better your health. If you don't write it down, look for patterns (in relation to the food you ate, meds taken eg Insulin dose), or if ur dr doest review the numbers, it is useless. But using the data to guide changes in ur diet and meds to keep bg within a goal may be critical to keeping u healthy.

Monitoring treatment: Testing blood sugar, before meals, can provide an indication of the effectiveness of treatment of diabetes and serve as a guide for the dose of medication to be used. It is especially important in Insulin dependent diabetes. You should consult your doctor about the finer points of glucose control.

Depends on treatment: Knowing what your blood sugars are at different times of day will 1) teach you what makes your bs go up and down, 2) provide trends that can help guide therapy, and 3) keep you safe before exercise, driving or sleep (is your bs a little low, do you need a snack).

Diabetes: Check your blood sugar on alternating morning (before breakfast) and at bedtime the next night. Once you see whether the two values (over a week or two) are similar but high, begin to keep a closer eye on your meals. Check pre-breakfast, write down all food intake, re-check before lunch. If there is a big difference (higher at lunch) you should consider changing your breakfast diet.