I assume you have a rough idea what Google Tag Manager (GTM) is, if not, you may either read its official website, or watch the nice Introduction Video to get the brief idea.
Once you have a brief idea of it, it sounds like ‘Yeah! That is our choice and we need it to empower our marketing / site tracking strength and management.’ by marketer, or ‘Gosh! We have to implement it in order to off-load the work of various tag setup from IT Team to Marketing Team’ by I.T. Tech. I am a front-end web developer and often need to make suggestion / decision to confirm whether to go for an approach, and Google’s product often a nice choice to have, but probably not this time when I am writing this blog.
Somewhere over the WWW have people like blogger / SEO expert introducing GTM by coping / elaborating its good point (mostly the good points that mentioned by Google Tag Manager official website). But when you come to the analysis phase, you will find it lack of detail documentation to implement it when you need it a bit more advance.
My case is to start preparing the migration of Google Analytic (ga,js) to Google Universal Analytics (analytics.js) for my company’s E-Store, and I have no difficulty to setup the Containers, Tags, Firing Rules, Marcos for general site tracking using Google Universal Analytics tracking type. I can see the configuration I did in GTM start populating data to various report, mostly similar with what I can see in existing Google Analytics profile. However, for some case we need to have different tracking code with different value per several different page, then the problem I face is the grow of Firing rule. And the worse thing is, all the rules / tag are listed linear, without folder structure for organization.
Furthermore, leverage the tracking code deployment task from IT team to marketing team is not an ideal way in terms of site stability. If there is bug in tracking code and is being deployed without proper testing, the site will subject to the issue and the IT department often be the party who being blaming by site user instead of the marketing team.
I would advise IT team to implement Google Tag Manager to their website, and use it as a way to simplify their tracking code deployment, and keeping the account secret from non-IT team member, so as to avoid them from introducing issue to the site.