Re: USS Grandeur - One... More... Time!
They don't provide any meaningful thrust but they are the exhaust of the impulse fusion reactors so helium/other fusion products and probably a lot of heat are expelled from there which you probably still don't want to have near your nacelles and/or pylons.
"She's got to have a tailpipe."
"Sword is personal, brings slicing to a man, you getta that personal feedback, nuclear weapons?.. Meh, goes off big bang and you don't get any feeling.."