I've sumped three tanks so far, and the marine will be the fourth. So long as it's set up pretty well, you are laughing. You get the added security of a larger system and more area for gas exchange, so oxygen deficiency is lessened.
And in FW especially, you can throw a ton of media. I must have about 25 to 30 kg of Alfagrog working away on my 150 gallon.
For marines, it provides a great place to hide heaters, skimmers etc so that you have no wires going into the tank (except for any PH if you don't run closed loop)
Andy