[myTouch 4G General] Keldarr:
Check out this link it has all you'll need to know http://androidforums.com/evo-4g-all-things-root/210253-setcpu-guide.html

What you want is your device to throttle based on the load being put on it. When you aren't doing much i.e. reading a text it should be clocked at 245760 for example because that's not a demanding task. and versely when you play a graphics intensive app or something, it should use just over the maximum amount of cpu power needed to run the app so the app runs smooth. but wont waste battery by overclocking to 1708800 when only a speed of 1017600 is needed. For this i use "conservative" on SetCPU because it will allow more customization.

My advanced settings for SetCPU are as follow. i haven't use CPU Tuner but hopefully it's similar.

Sample Rate you want kinda low 200000 is what i have and i don't get much if any lag.

Up Threshold is at what percentage of processor usage that the clock speed is increased. for me its set to 60. in other words at 60% load on the processor it will start to increase the clock speed.

Down Threshold is the load percentage where the clock speed will be reduced. i have mine set to 33.

Ignore Nice Load will just ignore nice processes. This includes system i believe. i have mine set to 0.

Grabbed this from a mac forum but it should apply.

"A process's priority is determined with a complex formula that includes what the process is doing and how much CPU time the process has already consumed. A special number, called the nice number or simply the nice, biases this calculation: the lower a process's nice number, the higher its priority, and the more likely that it will be run."

Frequency Step is how much of a jump the CPU will take to meet the load. mine is set low, (12) because most processes and apps wont need a whole lot of boost to run smoothly. For my device on average it will be under 768000 which is what you want and is where the battery saving really comes in. Because the CPU is under-clocked most the time its using a lot less battery but is still running everything smoothly.

A lot of people set there devices to ondemand because it's, "very responsive." although true its responsiveness comes from big steps in clock speed as opposed to the small ones that will most likely get the same job done. i.e. a clock speed of 902400 is more then enough to run the process quickly ondemand will jump to 1708800 to handle the same task.

copied from the above link at android forums.

" * ondemand - Available in most kernels, and the default governor in most kernels. When the CPU load reaches a certain point (see "up threshold" in Advanced Settings), ondemand will rapidly scale the CPU up to meet demand, then gradually scale the CPU down when it isn't needed.

* conservative - Available in some kernels. It is similar to the ondemand governor, but will scale the CPU up more gradually to better fit demand. Conservative provides a less responsive experience than ondemand, but can save battery.

* performance - Available in most kernels. It will keep the CPU running at the "max" set value at all times. This is a bit more efficient than simply setting "max" and "min" to the same value and using ondemand because the system will not waste resources scanning for the CPU load. This governor is recommended for stable benchmarking.

* powersave - Available in some kernels. It will keep the CPU running at the "min" set value at all times.

* userspace- A method for controlling the CPU speed that isn't currently used by SetCPU. For best results, do not use the userspace governor."