Bug testing is super important if you run Multisite. After all, you want your network to actually work for your users. Imagine if you set up a blog at WordPress.com and had trouble setting up a domain or your theme kept resetting. Not cool, right? Now imagine if your users experienced similar issues on your network. Also not cool.
Whether you have set up a local or online site to test out new designs or plugins, it can be difficult and time-consuming to push changes to your live site. Pushing changes to a live site can also make it difficult to track and test bugs. And don’t forget how unprofessional it can look to visitors if they are using your site as you make changes here and there.