Keeping an eye on CO2 is really interesting. I recently moved from an apartment with an electric range to one with a gas range, and CO2 gets as high as 3000ppm when I'm cooking (compared to a baseline of around 700 or 800). I don't know what the effects of this are, but the monitor reminds me to ventilate during and after cooking.
(I have my Airthings monitor bridged to HomeKit with Home Assistant and it seems severe enough for Apple to send a notification to my phone about it, by default. So I open windows and am happy to be able to notice air quality issues that most people will miss. I did turn off the notification though, I know I'm cooking ;)