To RT and BUX, how difficult of a disease is it? I mean, do you have to stick to a strict plan like Domi mentions he sticks to, or just have to avoid eating/drinking certain things and it's something you can manage?
rt's answer is pretty spot on. You want your blood sugars to maintain between a certain level - usually between 80 mg/dL and 110 mg/dL when in fasting mode. Obviously when you eat, there is a natural rise in blood sugar, but if you are on a consistent pattern, you can actually see a very minimal amount of time where your sugars hang around 140-160, but then come back down.
Once you eat, experience stress, exercise, etc., it can change that blood sugar in a heartbeat. So, as rt said, it is about managing how doing XYZ or eating ABC will affect you in the moment, but also down line a few hours. And even the rest of your life.
Domi seems like he is trying to be on super tight control, which is the best course for a diabetic. His concerns are more with low blood sugars than high (I would imagine) b/c you may think you are playing 17 mins of ice per night, but then an OT game happens, and you see an additional 2-3 mins in the game. May not mean much, but if your numbers are slightly off, you don't have a post-game snack immediately, or something else, you could fall on the low blood sugar side (always more dangerous in the moment than high sugars). High sugars are also bad though and lead to the dangerous stuff later on (eye disease, kidney failure, etc.)
So for my answer, it is manageable, and not always easy. But the more that you stay on a strict diet or schedule, it does help both long and short term. That is why the pump is so good - now you can scale back insulin rates when exerting physical energy, so you have that control factor available. Whereas in the days when I was first diagnosed (1997), this technology was not even available. Hell, they had just started coming out with the spring-loaded devices to test your blood. Imagine having to p.r.i.c.k your finger with a pin willingly and not have any idea how deep you may go. That's always tough, and why a lot of diabetics (especially older) were not great with testing blood sugars. I think I am better than most, but Domi puts me to shame.