Another great feature to chrome-devtools is that you can follow the loading of your websites and the issues that arise (that do not function as expected).
When you have installed a script, sometimes it is not clear to see if it functions correctly or not. Or if you have been working on a Content Security Policy you want to see if everything still functions as it did before (believe me: it won't )
Google dev-tool will show every issue including the details of what went wrong.