I use the Animas (no longer available) and initially wondered something similar but wit ha different scenario - a few times, I was worried the pump was not working properly so "primed" the pump (like a pen airshot). The only way I could find to do this also requested a cannula fill which I know was not necessary. Then I realised that I could "fill" the cannula with 0.00 units and move on.
I am intrigued why you are changing everything apart from the cannula.
This is not possible for me because after a couple of days my cannula starts to itch.
I realised many people can last longer than I but surprised you are changing everything except the cannula.
(Although, as I said, I am not using the Insight so things may be different.)