Just where the new tank will go and what fish to get. My SO is very "I want this one" and I usually have to tell him "Gets to big, won't play nice with what we have, no room" and he whines. Since I do all the maintenance and he bankrolls (yay student life) it works pretty well. He decided the new 125g would be next to his side of the bed for instance. We both picked 3 places and the only crossover was that so it won!