In line checks, in training, what you see are perfect behaviours, because you know you're being checked; you know your licence is on the line. Furthermore, there is a very important component: there is a misperception that in aviation, safety is first, and that is not true. Safety is the result of a compromise between trying to achieve protection goals, safety, and production goals, because this is an industry.
The true professional in aviation is the person who has managed to accomplish this balanced compromise between producing—that is, achieving the organizational goals—while protecting. In training, and to a large extent in checking situations, you're only interested in protecting, in the safety component. There is no production pressure. That is why training behaviours are only an indication of what real life behaviours are about.
By deploying systems that capture real time performance, you are capturing realistic operational behaviours, not idealistic behaviours, because then you're capturing how people manage this compromise between producing and protecting.