People do have access to privileged information and that will influence their decisions on both conscious and unconscious levels. It's not possible to detach yourself from work completely and asses your thinking whether it is influenced by something you saw or not on an objective level. It will also be difficult to prove. For example if an employee hobby is trading, how do you prove that the trades they made are based on their own independent research or based on what they saw? If they saw something that could make them money, they could easily create a trail of evidence that they researched the matter on their own - it will be difficult to prove that it originated from looking up the privileged information and unless someone is going to be making millions, it's frankly not economical to commit resources to. It is also in the interest of the company that such incidents don't see the light of day.