Every contest I ever did, I always had a trainer(some of the best at the time) insulin was always lowered and ultimately removed. Possibly reintroducing it during carb up. I'm not giving you advise, I'm only telling you what I did, was told to do by, probably the two best bodybuilding trainers at the time. I did the Jr. National in 1998 as a middleweight came in 2cnd but I only weighed in at 166. The weight class cut off is 176 and a quarter so I had a whole lot of muscle I could put on and remain a middleweight. I was definitely the smallest in my class but I was also the hardest and most symmetrical. I wanted to do the USA in 99 by I knew I would get destroyed if I came in at 166 again. So, for a year I worked with Chad Nicholas to just put on as much muscle as I possibly could. I used GH for 12 months consecutively, for the first time in my life, was using 4 ius a day. It was called I think Serostim, it was made in the US for aids patients and they all sold it to bodybuilders back then. He also had me taking humin R started at 5ius before breakfast and 5 ius post training. That eventually was upped to 10 ius and 10ius. At about 1werks out he told me to stop the insulin and we never used it again. His reason was it made it harder to get into the kind of shape I usually do on insulin and he'd rather me come in harder than bigger. I added 25mcgs of t3 to the GH and never used insulin again (that was my last contest). I weighed in at 172 and came in 6th, which I was really happy about. When I looked at these guys backstage I almost went back to the hotel. Guy named Jonny Stewart win the class, I still have no idea how he was a middleweight he looked like a damn heavyweight to me. Danny Hester came in 5th. That was kind of cool because I always admires his look and he only was ahead of me by 2 points. It's amazing he's still at it at a high level.
So, to answer your question, I would ask your coach what his reasoning is for sticking in insulin now, when you've never used it before? How far out from the contest are you? He could be trying to put a bit more muscle on you, if you still have some time. I would talk it over with him though.