why does HR's network need to be accessible from the same internal network that everyone else is on? Convenience I guess. Every book I've ever seen on network

why does HR's network need to be accessible from the same internal network that everyone else is on? Convenience I guess. Every book I've ever seen on network design and system administration talks about "departmental" servers and segmenting corporate networks at functional borders, but in practice I've never seen it. It's hard enough to get people to use different network shares for different data (e.g. personal, departmental, project related) instead of one global, world-writable share. This occurs at every level, from small businesses to the largest corporate and government networks. On top of that, even if you compartmentalize, there really isn't any technical method to prevent Sally in HR from emailing a list of personal email addresses, phone numbers and addresses to Sam in the Communications department so he can send out Christmas cards to everyone. And, Sally being a non-technical user will probably just "hide" the social security and salary columns in that spreadsheet instead of deleting them and then will blame Bob in IT when that list of salaries ends up on the global network share and eventually printed out and taped to the wall in the hallway.