What purpose does a control area really serve related to managing air traffic flow?
The main purpose of controlled airspace is NOT to &quot;streamline&quot; traffic, but to protect traffic. Control areas are not there to &quot;service air traffic service personnel&quot;, but to enforce certain rules upon the pilots.
In and around busy airports, the density of aircraft in the sky is relatively high, meaning there would be a relative high risk of collision if everyone were just flying around randomly. To mitigate this risk, various types of controlled airspace is established (control zones, terminal areas, control areas etc.)
Within controlled airspace, aircraft are subject to an ATC clearance, which more or less eliminates any risk of collision. Crucially, outside of controlled airspace, pilots can, essentially, fly pretty much however they want, and the only way to not hit another aircraft is if you happen to see it out the window.
Control areas are not just established around airports, but in any area where the density of air traffic is high. Typically, this means pretty much everywhere at higher levels, and around major airports at lower levels.