Good points:
* Castles provided a secure base for William and his followers in a newly conquered land.
* They helped to control the local population and prevent rebellions.
* Castles served as administrative centers, housing courts, prisons, and other government offices.
* They were also important economic centers, generating revenue through tolls, taxes, and trade.
* Castles could be used as royal residences, providing a safe and comfortable place for the king and his family to stay.
Bad points:
* Castles were very expensive to build and maintain.
* They could be difficult to defend, especially against a prolonged siege.
* Castles were often unpopular with the local population, who saw them as symbols of oppression.
* Castles could be unhealthy places to live, due to the lack of sanitation and the presence of disease.
* Castles could be easily used as a prison, housing and punishing opponents in dangerous conditions like a tower.
Overall, the castles that William built had both positive and negative impacts on England. They were essential for securing his power and control over the country, but they also came at a significant cost.