Which does have a purpose. If the camera looks into the room, the audience has to know that someone is hiding to get the point.
Doctor Who was a bit clumsy about it at times, but it's still a problem. You don't have to reveal the main villain's motives (but then I've already held forth on that, here), but sometimes you do. Except that frequently you have to hide a fair chunk of them for suspense reasons. . . it's when you have to reveal that the villain, or someone else, is hiding something, but not what.
In an omniscient POV, the narrator can tell you. Then, in an omniscient POV, the narrator can tell you everything and has to have the rhetorical skills to convince you that he reasonably told only that something was hidden, but not what it was. (Some great writers have failed in that; Wayne C. Booth's Rhetoric of Fiction has some interesting stuff on it.) In more limited POVs, there are fewer techniques, but they can be deployed more reasonably.
And when dealing with MacGuffins of magical ability. . . things can get really interesting.