What are you trying to do with it, is what I'd be asking myself.
My primary goal is to stop buying weed, so I've got a veg tent and a flower tent setup to be a perpetual grow. With another tent, and a removal of legal restriction on plant numbers in my state, I'd maintain a mother tent so I could keep prized genetics around forever.
There's a part of me that wants to get into the hobbyist side of it a bit more and start breeding my own strains, but that seems like a lot of work and I'm not sure if just having 3 tents would be enough for that... Perhaps you could just use one for males? It's something I haven't researched enough to say for sure, but it's a possibility.