Technology often benefits us and sometimes we become it's victim. I recall years ago when I was assigned to the narcotics unit, we had begun recording street transactions on video cameras concealed in the car and aimed out the driver window. Drive up, bad guy approaches, sells dope. This became so common place that eventually the State Attorney's Office did not want to prosecute a case UNLESS it was captured on video tape.
Both dash cams and body cams have advantages. Again, while dash cams often caught bad guys in incriminating acts, confessions to crimes etc., there have been instances where officers sacrificed tactics and good practice in the name of keeping everything immediately in front of the camera.
Body worn and especially head mounted cameras give that "POV" perspective, but often still do not tell the entire story. Think of this, NFL referees will use camera shots from several different angles to determine what happened during a particular play, yet we will often times use a one and only available camera angle to judge another Officers actions.
"If you are ALWAYS ready....you never have to GET ready....."