To expand on the above:
The pump knows (1) how much insulin it’s delivered (2) how many carbs you have entered (3) what the CGM reports. That’s it. That’s all it knows. It then calculates how much insulin to give you based on those three things and your current settings (carb ratio, correction factor, etc.).
If any of those three things are inaccurate, the pump will make the wrong delivery decisions. Sometimes when I insert a new Dexcom sensor, it reports a false low. The pump then lowers or even stops my insulin delivery based on that inaccurate reading. I have to turn off Control IQ for a few hours, calibrate the sensor, wait for it to get on track, and only then turn Control IQ back on. Otherwise, I end up with a really high blood sugar because it takes several hours for the CGM to correct the readings. Sometimes when I eat a meal that’s high in fat, my blood sugar goes high because I entered the right number of carbs but my digestive system is breaking the fat down into additional carbs. The pump’s correction boluses aren’t enough and I still feel full. So I need to carefully give myself an extra bolus to correct for the additional calories I’m still digesting that the pump doesn’t know about. If the cannula comes loose, the insulin drips away instead of being delivered and my blood sugar goes high. Sometimes I don’t notice that until the pump alarm tells me that I’ve gone too high and automatic correction boluses (and/or increased basal insulin) aren’t working. I have to replace the cannula, but then the pump’s Insulin On Board calculation is off because I didn’t get the insulin it thinks I did. So I need to do a manual bolus to make up for it, and it still takes time for things to get back to normal because the IOB will remain inaccurate for hours after.
All of which is to say the pump and its algorithm aren’t perfect. There’s a lot that it doesn’t know. And if you give it the wrong data, it’ll make the wrong decisions.
Case in point: If you disconnect from the cannula to take a shower and you don’t suspend insulin delivery, the insulin will drip out instead of being delivered, the pump’s IOB calculation will be off, and it will make the wrong delivery calculations.
Granted, in most cases, that’s probably going to be a small thing. If you’re in the shower for half an hour and your regular basal rate is 2 units/hour, then that’s only 1 unit off. You’ll maybe run a little higher for a while, but eventually the numbers will even out and it won’t matter.
Sometimes, though, the pump will attempt to deliver a correction bolus while you’re in the shower, and it has no way of knowing that the dose is going down the drain. And then its calculations will be off for several hours.
So, in most cases, it probably doesn’t make a significant difference whether or not you suspend delivery for half an hour. But there’s no benefit to not suspending delivery during that time and not only are you wasting at least a small amount of insulin, you’re risking the pump being inaccurate for hours. It’s best to follow the guidance of the official instruction manual and just suspend delivery for a while.
As for charging the pump: If you connect the charger, the pump will charge. Regardless of whether or not delivery is ongoing and regardless of whether or not the tubing is connected to the cannula.