Previewing and submitting changes
Google Tag Manager injects code into your website, which is an inherently risky thing to do if you don't know what you're doing. Fortunately GTM comes with a built-in preview mode so that you can test everything before making it live on the site.
It's also very easy to enable and disable triggers and reverse changes you've made, all via GTM. If something unexpected happens or a problem is spotted, there's no need to contact your external web developer with all the associated costs and delays. Everything can be controlled in GTM.
As long as you know how the preview mode works you shouldn't run into major problems. Let's take a closer look: