I don't know how this works for single player, but in multi-player each character choses a family trade, and if that family trade isn't chosen then your town is without that trade. For example, I am a merchant, another person chose blacksmith, another chose alchemist, and another chose fisher. After a couple of days we realized our fisher didn't want to play as much as we did so we replaced him and this new person chose to be a rancher, but the fisher's family remained in town.

The other day we realized our town had no tailor, so we made a tailor character to go unused, and his family promptly moved in to town ready to provide us with his services.

So now our town has everything we need. Its neat.