LOL! Well, more water equals more stability so people will go with the biggest sump they can fit to add more volume to their system to provide them with more stability. Other than that, like you mentioned, a sump is a good place to hide equipment like skimmers, heaters etc. Also, it can be used as place to house a macro algae in a refugium section for nutrient export as well as add extra flow to the tank via the return pump. I agree though, people use to use sumps for bio-balls in a wet/dry environment, but as well all know, wet/dry's are nothing but nitrate factories as their end product is nothing, but nitrates as they have no way of performing denitrification. Then people started using live rock for like the Berlin method etc which is effective, but then some tend to get tired of having to keep their sumps clean as well so they removed the live rock (like in my case) and just rely on the rock in the display to do all the work. Just think of sand beds these days. People use to run nothing but deep sand beds or shallow sand beds, but bare bottom tanks are getting very popular. Why??? Because it's easier in a way to keep a clean tank without all the waste that can get trapped in a sand bed as well as you don't have to worry about sand storms from too much flow or a sand bed crash. I never had a nitrate free tank until I lost the live rock in my sump and went bare bottom. In any event, you have to go with what works for you. There's no one way to go about things in this hobby
Aren't sand beds used for denitrification as well though?
I was reading somewhere, that someone had come up with a method of a remote deep sand bed in a 5 gallon bucket or so. They were using this for the denitrification.
Granted I have taken to heart with everything..Do what works and don't depend on someone elses advice as gold to fix your problems. However since I dont yet know how to ask the appropriate questions to solutions I don't know the problem to, to start with. I start by asking for solutions and waiting for enough responses that someone like whats happened here will respond with the answer to the question I didn't know to begin with.....
I should have just started by asking what does it require to rid Nitrates. If Ammonia turns to Nitrite and so forth turning to nitrate. What rids nitrates. Is it the skimming? Is it filtering through the sand, the rock? is it circulation? All?
Biggest thing though for me being a newbie is not noticing any ill symptons from my fish or coral they all seem to do just fine. Colors and all. I however cannot keep and anenome.. (2) down and I will stop here till I find my nitrate issues.