Kernels in general topic

HI . One question. Im using a custom kernel and its cool but i wanted to ask you something about kernels in general .

In all the phones i've been using , no matter if lg , Samsung or Sony , stock or aosp . All the kernels (stock or custom ) work the same way .

Ir i dont touch the screen, its at 200 mhz and if i touch it , then it jumps to 600 until i stop touching the screen . It never uses the other values except 1200 sometimes . This way of going up and down the values eats the batery of all my phones . It is a solution or i im doing something wrong ?

Please someone help me because i dont know why the same bug follows me no matter the rom , kernel or phone