Is Norfleeting considered an effective strategy?

[PrinzMegaherz]

quantum_mechani said:
Madcastleing is pretty much standard practice late game with little else to spend gold on. But as far as building one in each province right after taking it, it slows expanding down to such a degree I would not recommend it.

Does it really slow expansion?
Mad Castling is very strong for nations that do not use ressource heavy troops like caelum. You can make use of a cheap castle like the watch tower to fortify all provinces while your mages/pretender conquer new ones