One of the improvements is memory optimization in functions. Microsoft says that there is an abundance of small-sized functions in web scripts. This is true, as it's a very common practice for developers to compartmentalize code for reusability.
Microsoft solves this problem by refactoring the metadata format in each function. For example, pointers that point to rarely used functions are "moved to a dynamic auxiliary structure".
According to Microsoft, most 32-bit counters rarely offer any values above 256. Because of this, most values can use only a single byte (for those that don't understand binary, a byte is eight bits; 11111111 equals 255 in decimal).
Normally, a browser would parse all of those event handlers when you load the page; however, most of those events never end up being used, making that method a waste of resources. Beginning with the Anniversary Update, Edge will now only parse the handlers that you use, in real-time.
All measures collected on 64-bit browsers running 64-bit Windows 10 Insider Preview
System Info: Dell Optiplex 7010 Intel(R) Core(TM) i5-3475S CPU @ 2.90GHz (4 cores) 4GB ram
It's interesting to see Microsoft testing its new features on older hardware, as that's Intel's third generation Ivy Bridge CPU, where the latest model would be the sixth generation, Skylake.
Source: Windows Blog