TL;DR
Google Tag Manager (GTM) is a Google product that helps SEO professionals gain much more insight into what is happening on a Website. GTM also provides a way to easily add tags and triggers as well as add things like Google Analytics and other SEO related software

I personally think that GTM should be used wisely. For example in a Blockchain PR campaign GTM can harm the campaign results since some readers who click on the link might notice the GTM which will make the article feel unnatural (the reader will understand that the company paid for that article and use GTM to measure the results).

Natural backlinks