One of the common methods through which tags hurt site performance is simply the fact that some tags are slow. Various factors impact the performance of tags, including internet router bottlenecks, server peaks for vendors using multi-tenant machines, usage of low-cost cloud services by vendors, and more. It only takes a single slow-loading tag to potentially slow down the site.
In order to illustrate this, consider the figure below, which shows a web page containing 4 tags, loading synchronously. Each tag on average takes 250 milliseconds to load with the exception of the second tag which takes over 2 seconds to complete. Because of this single slow-loading tag, the entire page now takes over 2.5 seconds to complete.
One method used to speed up this process is using asynchronous loading of tags. Another method is slow tag killing, which is the process of terminating the under-performing tags.
To demonstrate this, consider the figure below, which shows the same scenario with both asynchronous and slow tag killing methods added. In this case, the criteria for slow tag killing is set to half a second. With both features added, the load time is reduced by almost 2 seconds to slightly over half a second.
According to a recent study by Gomez, a one-second delay in page response can result in a 7% reduction in conversions. Knowing how every second counts, slow tag killing can be a valuable method for improving site performance and usability.