In the standard scenario of running an agent in a monitored public folder, an agent in that folder is routed by default to the script handler supplied by Microsoft® Exchange Server (the Microsoft Exchange Scripting Handler). But you may feel that scripting doesn't give fast enough performance, so you may want to use another handler in which event response code is hard-coded in C/C++. Or you may not want customers to see your source code, so instead of shipping scripts, you ship compiled code in binary format.