effect? Not totally sure what you are asking about, but you dont have to run carbon. Many people dont run carbon (like me) and I dont totally see a real benefit to using it all the time. Some people like to run carbon once a month to "polish" the water, but i personally think that is just removing the coral food. Some people like to run it because it can remove odors, but IMO a healthy, clean tank shouldnt stink anyways.
I can be helpful to run if you have some sort of toxin in the water, like from having a lot of leather shedding at once, but once again, not something you need all the time or ever.