System: if the actual system malfunctions, the cooling fans may stop working as well as cause the computer to overheat.
App: potentially incorrect information about the computer temperature could be displayed
Heat sink fans may be replaced throughout a computer's lifetime
Different fans have different CFMs and are not affected the same way
(e.g. increasing fan RPM by the same factor does not cool the same amount on different fans)
Switching to liquid cooling as opposed to fan
Cooling method would be different and incompatible with current design
The hardware components would be built into the computer, so its lifetime would be the same as the computer itself
The app can be deleted and not used if deemed unnecessary. The system information will not need to be stored either.