The pros- Save space, money, utility costs, plus, you can move them around, or out of town. Perhaps a solution for those who are homeless?
The cons- Kind of lonely unless you are willing to share space with partner, a very loving partner. Someone can steal your little house which recently happened to a woman who came back from shopping to find her house, gone. Fortunately, the little thing was soon found, along a country road, or something like that. Kind of hard to steal a house, of any size.
Of course, outside space is a must. For me, 100 acres will do.