Good reliable internal and external network connections are important.
As an organisation, project office or program office, it is important that both internal and external networks work well.
It costs a lot of money in lost time if the office connection to the internet is offline or very slow. Managers, designer, drafters, procurement, and many others need external access to look up supplier information, maps, site info, government websites, standards, definitions, dictionaries.
Blocking access to sites using Net Nanny or similar is better than blocking all external access.
Although the company might have to pay high bandwidth costs for a faster connection, that is probably cheaper than the lost time of people having to wait for pages to load.