From what I understand, the all-grain brewer warms up water to a particular temperature (usually 10-15*F over the strike temperature), adds this warm water to the grains in a mash tun, in an attempt to hit a particular temperature (around 145-160*F depending on the grains/style of beer), and then dumps the wort after an hour. I also understand that it is important to keep the temperature of the mash tun consistent at the desired temperature for this entire time; this is why a cooler is recommended for beginners.
However in a few YouTube videos, I've seen the all-grain brewer feed in a temperature probe into the mash tun and leave the cooler lid slightly ajar to allow for this. To an extract brewer like myself, this looks pretty silly, as the temperature would remain more consistent with the lid fully closed.
Is there a risk that (even in a cooler mash tun) the temperature might drop significantly enough to warrant additional hot water, such that measuring the temperature is more important than closing the lid completely? Or is there something else I am not considering?
At the same time I would LOVE to use my RaspberryPi to record this temperature. I'm thinking about drilling a hole for an airlock and feeding a temperature probe into the airlock (as I do with my carboys) to enable me to record the temperature of the mash tun while having an airtight environment.