Off the top of my head, the big IV mods I can think of are VisualIV and environment mod v5. I'm not sure if there are others like them, but if there are let me know.
Anyways, I'm a bit confused as to what exactly these mods do. The one thing I do know, is that they edit the timecyc files for more "realistic" weather and colors. Alright, that's understandable.
But lets take environment mod v5 for example (since the OP in the VisualIV topic doesn't really explain what VisualIV does). Environment Mod v5 says it fixes the shadow calculations and sun reflections. But what exactly is that doing? Why does that need to be fixed? What's the difference?
On top of that, people say that environment mod v5 and VisualIV can boost your performance a bit. But why? What exactly is it doing to give you some FPS?
I'm just really confused as to what the fuss is about these mods. If they're fixing things in the game, and optimizing it - I'd like to know how and why so I feel a bit more comfortable downloading it. I don't want to be missing out on anything that fixes GTA IV.