HI JasonKng -
Version 4.8 included a massive addition and performance improvements for Post Processing, read more here, and in particular a new Film Standard Tonemapper was added. In reference to the code comments, whether the Gamma only shader is at the beginning or the end, the Least Expensive Code will default to that Table Entry. Least expensive function actively searches the table each time. The Most common configuration for PCs are the most expensive post processing setup, while for Mobile the most common is the simple Gamma Shader, which is what the initial comment addresses.
There have been some issues with the 4.8 post process settings and the new tonemapper settings, but they are unrelated to this particular bit of coding and we are currently working on making improvements and many have been implemented in 4.9.
Thank You -
Eric Ketchum