This script is in charge of creating a "Log File," a .txt file that contains important info about each trial and can be used for analysis at the end of the experiment. This script is just the messenger - other scripts like ReplaySession tell it what to write.
It's written in C-sharp because that language allows "StreamWriters" to write to text files, and JavaScript does not.
This script should be placed in the "Standard Assets" folder because Javascript functions can only reference C-Sharp functions if they're compiled first, and the Standard Assets folder is compiled before the rest of the project.