Apparently every idea has been used when it comes to making TV ads. I say this because there have been waaaaaaay too many commercials featuring a dead theme. And by "dead", I mean "brain dead", as in the agency was lazy and uncreative.
Specifically, ads that feature "behind the scenes" of working at an agency. This includes brainstorming sessions, making the commercial, etc. Basically, any time you think it's a good idea to make it look like the ad was "brought to you by" the agency - it's not.
Please check your egos at the door, no one cares about your career or how you do it. In fact, most people hate you for wasting their time. Want to make an impression with your audience? Do something creative like Philips - sponsor a TV show or football game and don't run ads. That goes over well. And yes, they're a client.
Brand managers -- if your agency comes to you with a storyboard or deck that involves showing how ads are made or any of the aforementioned scenarios, it's time.