Metadata can make your information sharing and storage efforts great successes, or great failures. Metadata can get you in trouble with the law, or keep you out of such trouble. Simply put, metadata management is making metadata do more things for more people in more ways, more economically. You manage it through people who understand it, and who have and know how to use the tools of metadata management. Foremost among those tools are Metadata Registers, Dictionaries, Directories, Locators, and Search engines.
Metadata management is a key part of information management.
It may be all of information management in situations where information management focuses entirely and exclusively on information sharing. These aspects involve metadata, but they also involve much more, including business processes. If you have an information management organizational unit that really does agency-wide information management work, then metadata management belongs there. If you have such an organizational unit, but the real work of information management is being done elsewhere, put metadata management where the real work is being done. There's a legal side to metadata.