Working requires us to form social relationships with our coworkers to get work done. Oftentimes, we're establishing shared language, and working tempo with coworkers through "inside" jokes, and other human forms of camaraderie. Not only would it be unethical to stamp the social aspect out of our working lives–which make up the majority of our waking hours, and a gross majority of our social ties–but it would also be imprudent, since removing social elements from working relationships would cripple them. It is necessary, and desirable, that we socialize with our coworkers to some extent.
The firm pits individuals–and groups–against one another in competition. Even in an ostensibly friendly, collegial workplace, the zero-sum reality of budgets and headcount encourage workers to jockey for position and push difficult, or unprofitable work onto others. Surveillance like this enables the most manipulative to exploit secret knowledge of the social relationships that are, again, necessary throughout the firm. A secondary effect of surveillance is the chilling effect: trust and camaraderie are hampered by the knowledge that one's every word can be used against them without recourse.
Firms regularly use information freely given to prioritize workers for layoffs. Decades of "employee satisfaction" surveys have facilitated the efficient firing of dissatisfied, burnt-out or mistreated workers. Surveillance offers the same facility, at higher fidelity.
If you are an executive, and you want to maintain dehumanizing working conditions, surveillance is a necessity and a boon. As surveillance increases, our working life becomes more prison-like, and our society progresses towards private autocracy. What astonishes me is how giddily those who profess to love Liberty readily shed it at work.