On the con side, your employees may consider Internet monitoring a privacy violation. They are wrong, because it's your network, but that could be their perception.
On the pro side, you'll get much more granular control over how your employees use the Internet. Whether it's bandwidth or time restrictions, or ensuring they don't surf to unauthorized sites, you gain a level of control that you didn't have before. And obviously, if bandwidth is an issue, your choice is pretty simple. Enforce quotas using one of these tools, or get a bigger pipe.
This was first published in July 2006