What does `adb shell dpm set-device-owner` do?

Question

So I have been looking a lot into how I can save some battery life on my Samsung Galaxy S8+ (not that it is bad by any means) and so I've been trying and looking at a lot of different apps. Among these are Greenify, Island, Tasker+Package disabler, and Ice Box. And especially Ice Box has caught my eye.

But there is something about, how Ice Box is set up that I don't understand. If the device is not rooted (which mine isn't), you'll need to run the following in ADB to make it work: adb shell dpm set-device-owner com.catchingnow.icebox/.receiver.DPMReceiver.

I don't know a lot about shell commands, but as far as I understand this will set the App as device admin/owner (is there a difference?)? But this command for some reason also require you to remove all account when run, otherwise, it won't work.. - BUT Apps like Island also require device admin? But that can be set right on the device without ADB?

What is the difference and what exactly does that shell command do?

Answer 1

Google has noted here:

A device owner is a specialized type of device administrator that has the additional ability to create and remove secondary users and to configure global settings on the device. [It can be used] to take fine-grain control of the configuration, security, and apps on managed devices. A device can have only one active device owner at a time.

_{(Emphasis mine)}

So now you know why all other accounts have to be removed for Ice Box but not for other apps. You can add those accounts later, after making that app a device owner.

Also, if memory serves correct, once you set an app as a device owner I don't think you can remove that app. You would have to factory reset the device or use root access to wipe it out.