High End Performance : IndustrialCraft, Buildcraft, Redstone Power : all of these mods create new entities that interact in extremely demanding ways. On a large server, once there are thousands of solar panels, massive quarries, cactus farms, and so forth the requirements for the host go up enormously. This server is hosted on high end hardware with a professional host to make enormous creations possible.
Current Specs : e3-1230 CPU, 6 Gigs Memory, SSD
Currently, No other IndustrialCraft Server except for possibly Industrial Rage has hardware this good. This is costing me a pretty penny, but unlike IR, I'm free-to play.
More Possibilities for the things you create : I have installed more client-side mods that add content to the vanilla Minecraft game than pretty much every other server. I'm always looking for new mods to add.
You can affect the world through your own efforts : If you are clever, you can build automated factories that can produce nearly any item in the game automatically. You can automated many of the steps needed for construction of buildings. You can build automated defenses that work, electronic locks, and so many more things. You don't need Op powers, spawned items, or map editors to do these things in this world.
It doesn't mean it's easy - you need to supply fuel and materials and organization and so many more things to make your cantankerous contraptions work. I usually play on this server with a web browser open to the pages for the mods here open in the other monitor. Gameplay here is extremely complex, about 10 times more complex than vanilla minecraft.
