Comment by mrweasel

This may have changed, I last used Tag Manager 9-10 ago. You basically added a single Javascript snippet to you website, then you could inject other Javascript into the pages, using various rules. So rather than having to redeploy our site every time the marketing department wanted to add a new tracking or retargeting script, we could just add it in Tag Manager. I think is a great tool if you insist on doing these types of thing. You can also extract and transform variables, so all the customization required to adapt to each service could be done within Tag Manager, keeping your website simpler.

One major issue Tag Manager solved for us was that a bunch of these online marketing companies that have their own tracking pixels/scripts absolutely suck at running IT infrastructure. More than ones we experienced poorly written 3rd. party scripts would break our site. Rather than having to do a redeployment, to temporarily disable a script, I could easily pop into the Tag Manager console and disable to offending service.

Maybe Google Tag Manager has changed, but it was a good tool, if you where in the business of doing those sorts of things. I suppose it's also a clever way of blocking all tracking from a site by just stopping the Tag Manager script from loading.