Google Tag Manager is a free tool and service that anyone can take advantage on. You can get more data in Google Adwords and Analytics as well and get track of other events of your site such as social shares, promo subscription and more. Any website can gain control over the tags that were added to the GTM and or to the snippet of codes being installed within the page container to track any event and usage being set in the tool.
The GTM implementations might as well include the tag migration from the different analytics. With this, it’s all necessary to identify the events in tag manager to trigger and which tag to add and or fire. The proper way to approach this is by defining events and custom variables in Tag Manager and triggering them from the website. Tag Manager then receives the event and outputs the appropriate tags based on rules which you have set up against this trigger.