A great example is The Flintstones and other Hanna-Barbera cartoons in the '60s specifically. If you notice when a character is running, you'll see the same background being repeated over and over. Eventually, audiences caught on to this, and it became somewhat of a joke for characters to mention it (4th wall break). Oh, and let's not forget those old sponsor ads featuring the characters smoking cigarettes, back when advertising such products was allowed on TV.
I can't find a clip on YouTube because of the episode name being super generic, but in the Season 4 Simpsons episode "The Front", there is a scene where Bart and Lisa walk through the animation wing at the Itchy and Scratchy production studio. The background is noticeably repeated over and over. Lisa is impressed by what she sees, leading company CEO Roger Meyers Jr. to reply regarding how most animation studios "reuse assets" to combat budget restraints. It's hilarious in context considering what is actually happening on screen.