The moment my pc or a server gets heated up after running all day long, I restart the pc. It not only clears the software lags by doing so, but most of the heat gets dissipated by this move.
Then you have a cooling issue. Rebooting doesnt fix it, it only cools your system back down to allow you to run it again.
During a reboot the total heat load will usually increase as hard drives spin down and back up and any CPU power scaling is ramped back up to 100% during the boot. The cooling that takes place during a power off is minimal if it is less than several minutes. Without power, the fans dont run and the heat is slow to dissipate. The benefit you see is from the OS being reloaded and not the resolution of a hardware issue.
In fact, powering off your system and letting it completely cool down only to power it back up will eventually lead to a failed CPU due to temperature stress fractures on the CPU core caused by repeated hot/cold cycles.
Powering off your computer will not resolve a hardware problem. The idea that rebooting resolving an issue indicated a hardware problem is simply incorrect. That is an indication of a software issue