It has its pros and cons.
Some pros would be that your employees would be able to access important information such as Emails, Information, News...etc and not just Local stuff.
Cons would be they can spend time doing useless things such as Videos...Instant messaging...THEY CAN DOWNLOAD VIRUSES. But if you have a good Antivirus, that shouldn't be a problem.
But again, the Pros beat the cons in this case.