TC and Temp Regulation mods serve several functions. They use exotic wires with very low resistance, Nickel Ni200 and Titanium, these wire have a significant shift in resistance as they heat up that can be detected and calculated against to make a calculated guess what temperature they are at. Using that calculation the firmware can a lot of times also detect when you are low on liquid.
Still the main reasons Evolv came out with the DNA40 board was another flare up discussion of diketones (Diacetyl and AP) as well as formaldihydes and acroliene gas being in liquids or the vapor aerosol due to dry hits and such, so thus TC was born. To control toxins like formaldihyde and a lot of times though no diketones are in the flavors put into liquids, once a liquid reaches a certain temperature these flavorings mixing together at said temp could also create D/AP diketones, keep the liquid under this threshold, the diketones do not form unless the diketone is already present from the get go. When it comes to dry coils, here is where formaldihydes and acroliene gasses were being formed from the breakdown or wicking, and/or breakdown of VG and PG at extreme temperatures, thus if you can throttle the temperature at the coil from creating any of these states you could control the what is actually in the vapor aerosol and bad stuff from ever forming.
So...
1) Control diketones and acroliene gas from forming at certain temperature thresholds
2) Control formaldihyde from forming from burning dry wicking
3) Control flavor and fine tune the output even further
4) Keep from having dry hits