fuel based generators produce smoke that pollutes atmosphere and dirt several chunks around it(different level for different fuels). grass does not grow, trees die out and acid rain falls in the area. The more smog there is the stronger and more wide spread the effect is.
machines like extractor or macerators produce small amounts of waste that also slowly accumulates in the environment, making it incapable of sustaining plant and wild life.
nuclear reactors produce nuclear waste( MinecraftSlime ) that should be securely stored underground - it kills plants all around the reactor area or the storage area (and spawns mutant slimes or smth ). reactor components can also become "used up" in the process and must be disposed of just like the nuclear waste.
battling the newly made pollution is another "fun" consequence that adds more to the game (although i hate cleaning )