Congratulations on a great and useful purchase.

Monitoring ambient can be very useful, particularly if you are water cooling your rig.
Case temperature is also useful.
Can't have too much knowledge of your PC's environment.

close to the feet, in the PSU chamber, there's openings where you can pass the thermistor to hang off the case

A common use case for this thermistor is to control the fan depending on the delta between ambient and water temperature (water temp - ambient temp).

That's basically the temperature that defines how efficient your radiators are. the higher that temp, the better they dissipate heat.

If you control your fans purely from water temp, you l'll have them run fast in summer because water is warmer... but the ambient temp is warm too, so they dissipate peanuts.
Controlled by water - ambient temp, the fans will only speed up if the computer is actively being stressed, and the fan curve is basically auto-adjusting all year long. Set and forget