Async or "Classic" Google Analytics
Async allowed tracking to run while the page was loading, where the previous version hurt performance because it delayed page loading. In addition, even short activities were tracked more accurately than before. A couple of years later, multiple dashboards were layered into Async, with more custom report options and a much more user friendly interface design. Subsequent updates included real time analytics and goal flow charts.
Of course Google integrated its Adwords (Paid Search) product/service into GA such that online campaigns could be reviewed in terms of landing page quality and conversion goals. With use of the ecommerce integration and real time analytics, tracking of online sales activity and performance became significantly enhanced (transactions, revenue, other metrics). The dashboard style presentation for general users, coupled with the ability for data analysts to drill deeper into the data further improved the product.
Async certainly provides tracking capabilities that will support decision-making, but it’s over 6 years old and you are missing out on some of the valuable tools Google has included to keep pace with, and lead, growth in analytics.