CPU power management

I've never given any thought to this, probably because I don't use or want to use laptops. But a thread here recently, which I can't put my finger on now, mentioned running the CPU at 100% all the time, which would burn out the CPU.

How is CPU speed controlled - in UEFI firmware or in the OS? Are there options in Slackware to regulate CPU frequency -- and fan speeds, while I'm at it? Or should I leave it to UEFI / CPM ?

All desktop-agnostic recommendations welcome.