A tag manager starts as a clean way to add tracking without touching site code. Within a couple of years it usually holds dozens of tags, and no one can say what half of them are for.
Adding is easy and removing is not
The point of a tag manager is that a marketer can add a tracking snippet without a developer. That removes the friction that used to limit how many tags a site carried.
Removal has no such convenience. Deleting a tag requires knowing what depends on it, and nobody wants to be the person who breaks a conversion feed.
So tags accumulate. Every campaign, vendor trial and agency relationship leaves one behind, and the pile only grows in one direction.
Ownership disappears with the people
Tags are usually added by whoever needed them, named however that person named things, with no record of purpose. Then that person changes roles or leaves.
What remains is a container full of entries whose names mean nothing to anyone currently employed. The safest assumption becomes that everything is load-bearing.
A naming convention and a short note on each tag costs a minute at creation and is the only thing that prevents this, which is why so few containers have it.
The performance cost is real
Each tag fetches a script from a third-party server, and each of those may load further scripts of its own. The browser has to do all of it while trying to render the page.
Pages get slower as a result, and page speed affects both conversion and search performance. The cost lands on revenue rather than on the marketing budget.
Because the degradation is gradual, it is rarely traced back to the container. The site is simply slower than it used to be and nobody can explain why.
Duplicate tracking distorts the data
Trials, agency handovers and platform migrations frequently leave two copies of the same tracking active. Conversions then get counted twice.
Inflated numbers flow into optimization decisions, so bidding and budget allocation are being driven by a number that is wrong in a direction nobody suspects.
The discrepancy usually surfaces when someone compares the platform's count against the order system and finds a gap that does not close.
Auditing the container properly
A useful audit works from the outside in: capture what the page actually loads in a browser, then match each request back to a container entry.
Anything firing that cannot be traced to a named owner and a current purpose is a candidate for removal, paused first rather than deleted so it can be restored.
Doing this once a year keeps the container legible. Doing it only when the site becomes unbearably slow means doing it under pressure, which is when things break.