The founder of an enterprise IM startup recounted this anecdote: "While deploying our IM software at a hedge fund, I noticed the admins using AIM, and suggested to an admin that the new intra-office IM system for the traders would be helpful to the admins as well." Her response: "Will my boss be able to see what I've written?"
The answer was yes, of course. One of the reasons the firm bought the app was to improve knowledge retention. The lesson here is that employees are averse to the vision of a manager peering over their shoulder when they're alone at the keyboard. If they know that it's merely possible, they will curtail their efforts, per the philosophy The Less Said the Better.
The PC, for all its deserved reputation as unmanageable, is a personal sandbox in which an employee doesn't feel constrained and watched. She is free to play with ideas and drafts, and chooses what to circulate to colleagues. That freedom is a boon to productivity.