[launchd-dev] Start a process on behalf of launchd

Hello What is the correct way to launch a process not fork'ing and exec'ing, using launchd instead? I've been reading a lot about how is it more secure, more reliable, and just better :) Should i necessarily create a *.plist file to a /Library/LaunchAgents/ directory, and then after i launched a process, delete from there? Can it be only launched via NSTask'ing launchctl or maybe there's some kind of API for doing such things? Thanks