Oracle Enterprise Manager is designed to help you monitor and maintain servers and systems in large scale enterprise environments and not so much to be used within a small company with only a couple of database servers. You can use it however if you look at the way the products is build you see that the intention is to deploy and use in large scale. When you are talking about maintaining large number of systems for multiple departments or even for multiple customers if you host and maintain systems for a large number of customers.
When you use it in such an environment you would like to store more information about the system than you get from a discovery. If you go to “target setup” and select Properties you can add more information to the target.