WordPress Multisite is powerful configuration of WordPress which allows you to run multiple websites, sharing a single WordPress installation. I think most developers tend to use WordPress Multisite for use cases which really should be separate installations. I know I have. If your considering using Multisite on a WordPress project, ask yourself the following.
Are all of the websites for the same client?
If not then stop right here. Since every website on a Multisite shares the same installation, things like database and FTP access are also shared. Coming up with clever ways to work around this may consume a large amount of time and resources.
Are all of the websites using the same theme or set of themes?
Each website on a Multisite can use a different theme. However, if all of your websites are using a separate themes then it could be a sign that you should use separate installations.