It changes resource spawning to be region based - by default regions are big which promotes using of trains. Resources will be more sparse so more logistics will be required to supply your base. As a bonus resources further away from start location will be more rich.
RSO also controls spawning of biter bases to make it easier for a player to move further into the wilds, but don't expect resources to be biter-free.
Mods that don't modify resources should work without problems. Support is present for most of large mods (DyTech, Bob's mods, Yuoki industries, Uranium power) and some of smaller ones. NARmod support is planned.
If you receive information about not supported ores (will be printed after game start) please post them in feedback thread along with information which mods are used. I'll try to add support for those mods then.