It is really important to our healthcare providers because that's how they measure how well THEY are doing in keeping people with diabetes healthy. It's a global measurement and so they can use it to compare their service to services in other countries.
For us, the individual with diabetes, it really doesn't have that much value. You might feel differently but for me, it's just another number, one of many that I use to manage my type 1 diabetes.
I have had a good HbA1c for a number of years now. But there was a period of time a couple of years ago when I had an excellent HbA1c of 48 mmol/mol (6.5% NGSP unit). However, both myself and my endo were confused because my blood glucose readings told a very different story. They were ALL OVER THE SHOP!!! Not one of my BG readings was within any of my targets!
We figured out that I was having more than the occasional hypo during the night and not waking up (Flipping scary). These lows were offsetting the highs during the day, making my HbA1c appear excellent.
These days, I look up my average blood glucose reading over 30 and 90 days on my meter. Plus, I look at my "standard deviation". The Standard Deviation SD is a measure of how spread out my numbers are and it's measured in a percentage.
The SD from the example above is +/-7 which is quite a spread.
Ultimately, I want to smooth out the peaks and troughs of my blood sugars and that's why I would like my average blood glucose reading to be between 8 and 9 mmols and my standard deviation to be a small as possible.
I was always tempted to brag a little about having reasonable HbA1c results. But once I learned about SD it removed all temptation.