They were the episodes that "no parent could miss". The "very special episodes". They're passé now (could you imagine "A very special episode of ... 30 Rock"??) but it seemed like every sitcom in the 80s and 90s had them. This video strings together some of the very best awful "very special episodes". Take a look!
I'd forgotten that Tom Hanks was in Family Ties! And in Philidelphia-serious mode too.
There are so many more very special episodes that could be added to this. My personal favourite was the episode of Diff'rent Strokes with the then-First Lady of the United States, Nancy Reagan talking to Arnold about "just saying no" to drugs. I hope a sequel or extended version of this video is released soon.