I love WordPress Multisite. It allows you to get a new WordPress site up and running within minutes. Especially if you’re a developer and want to test a new theme (version) on a plain installation, this is really handy. Or if you are a company and you need a new site, e.g. for a project.
WordPress Multisite works with both subfolders and subdomains. Subfolders are sites created at domain.com/newsiteslug and subdomains are subdomain.domain.com.