If you have a good spot, a SINGLE early campus is good, because you get it so early in the tech tree that they are still cheap like 60-70 production, if you delay too much and get some techs before it, the production cost skyrocket and becomes ineficient to grab that campus again, you would get better results buying workers, settlers, comercial hubs and city center buildings.
Well, that is my impression of it so far. The biggest increase you feel in production cost of districts is from early game to medieval era because there is a lot of important tech you have to grab and since the increase is linear with tech unlocked, the cost easilly doubles from the starting 60.
My hint is to imediately plant it down when you unlock it, so you lock the cost before it increase. This way it still is worth building, even if delaying by going for other stuff first.