Because parsing isn't free. In addition, one interesting optimization it opens up is something akin to the JVM where performance improves as profiling of code i

Because parsing isn't free. In addition, one interesting optimization it opens up is something akin to the JVM where performance improves as profiling of code is done. Imagine if every site that used a Javascript library served to improve the performance of that library for all future invocations. That would be nifty.