Big scale effects require usually more than one FFX. Having a lot of FFX and holdout objects asks for a lot of memory. Limited memory means rendering in passes. Different lights and shaders per pass multiply the renderpasses again.
To setup a render, it takes some steps and usually you forget one and need to resubmit. That's why I wrote this script, that overviews everything and gives the ability to set it up fast.
I avoided using .NET intentionally, because in big scenes it sometimes takes a long time just to open a scripted tool.