Just cause your screen is off doesn't mean your cpu is off, depending on what apps you have installed, if alot auto sync or have poorly written code that continuously use diff android processes, your cpu frequency might fluctuate while screen is off, you could use set cpu to control this. You could set alot of other different profiles such as underclock when phone is running hot, when its low on battery. It always depends on the user's usage but cpu profiles can help.
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