I work in tech so it is kinda embarrassing for me to ask this question but I never quite understood how something as simple as a power drain can solve almost all problems with a device. I use power to drain all the time, as the first troubleshooting step once we get our hands on a malfunctioning device but never quite questioned how until now.
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Most machines are tested very extensively from an off position. Most machines are not tested nearly as extensively when running for an extended period. As machines run, they accumulate errors, as something or another malfunctions in extended use. By turning the machine off and putting it in its base state, you get it back to where it was designed to run from, which, if nothing permanently died, will get you up and running.
When a computer is running everything is stored in ram. This keeps track of the current state of the device. Now if something bad happens to that current state than the device may operate in a bad way. RAM only lives until the power to the module is cut off so unless your computer saves it’s current state to disk and tries to recover from it on a fresh boot all of the ram is reinitialized to a start state. This allows the device to resume functioning because this initial state is predetermined by the software, and will not have any of the inconsistencies of your previous operating state.
I will assume this isn’t talking about a reboot, but more about actively draining the power in a device. The question isn’t very clear…
As others have stated the goal is to get the machine back to a pristine “known” state. The most common known state is at boot. There are a couple reasons why one would want to drain any residual power in a device:
1) Any well designed circuit board will have numerous bypass capacitors. These act a small little batteries next to components. They provide a local resource to quickly grab all the power it needs instead of grabbing it from the main power supply–longer traces have more impedance which makes changes in current slower. More importantly, your power supply will have a few large capacitors to filter the output current and make it nice and smooth. These can hold significant charge, and can power the device for several seconds (this is why every IT script includes turn the device off for 10 seconds before powering it up again).
2) Much less likely, but there could be some elements of the circuit that consume very little power but can contain a state that you’d want reset to get it back to the known state. This is much less common now with the advent of FLASH.
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