When Google released gtag.js, the new, global tracking library designed to (eventually) replace analytics.js, many Universal Analytics practitioners and users were confused (see e.g. Jeff's great overview here). It seemed like gtag.js wasn't really solving any immediate problem, since analytics.js had done a bang-up job with Universal Analytics tracking for all these years. However, gtag's modus operandi is the ability to leverage the same semantic information (distributed across dataLayer!) across a number of Google products, starting with GA and AdWords.
(Last updated March 2014) This post is the final chapter of a trilogy. The ultimate refinement, if you will. It all started with my foray into the murky waters of context, when I tested how weather data could be used to provide extra information about site visits. When I wrote that post, I had two trepidations: 1) does sending the API call with every single page view affect site performance negatively, and 2) does forcing the page view call to wait for the API call to complete affect the quality of visit metrics.