they help filter dirty water,bring down your nitrates, help animals make nest and good areas to hide in. but the bad thing is that shrimp farmers are taking 1/4 of the vegetation that mangroves live in so that's the bad stuff but mangroves are pretty good for theenviorment. If you need anymore info just go to wiki or just type in why are mangroves important.
I spray them every third day with rodi to simulate rain and wash down the salt creep. I keep them in my fuge i dose a little extra cal for them. You can ask other prople that have them they help out alot. Some people kep alot of mangroves and dont use a skimmer.