Great Merchants: I must confess that by the time I get a Great Merchant, I'm generally either pretty badly disliked by most of my neighbors or I've already set up trade deals that keep them constantly on the verge of bankruptcy, so I've never really been in a position to do a Trade Mission. I find them really useful when I have a city built in food-marginal terrain (generally sited specifically to harvest multiple different special resources). When a Great Merchant joins a city as a superspecialist, you get a sizeable money boost *and one free food*. That can make the difference between a city that can't grow to meet its full production/commerce potential and one that can.