Instead of managing separately Google Adwords, Google Analytics, ... you can control all of them through Google Tag Manager site when you use the Magento extension to add it into your website.
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Compatible with: CE 2.0 - 2.1.x
In order to apply Google Tag Manager for your store, only need to insert Google Tag ID, which you get from creating Google Tag Manager account from https://www.google.com/analytics/tag-manager/, into the Magento Admin and then, enable it to use. It is so easy and simple to reach such awesome tool only with Magento extension
As usual, for Google Analytics or Adword, you must put many codes on the source of website and the speed of your site is lower than normal because it is hard to load. However, with Google Tag Manager, it is called as the third-party to handle all your script-tags and you only need to add its code into your site.
Remarketing from Google Tag Manager allows showing your ads again and again to people who visited your site and click on them. With the remarketing program, it is fantastic to take visitors come back and get your offers they have missed.