Let's say you are a smaller department within a University and you want to manage your own machines, for any reason. Wouldn't it be nice if you had one console to look at that told you the status of your servers, even if there are only a handful of them? What about your desktops, are they patched? Do you know?
That is one of the scenarios SCE was designed for. You can learn more from the FAQ on the SCE Wiki.
Link to System Center Essentials Wiki - Frequently Asked Questions