These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Periphery Demographic: The movie was intended for a teenaged/adult audience, but has seen glorious success as a trippy way to introduce kids to The Beatles' music.
John claimed in one of his last interviews that while raising Sean, he and Yoko deliberately tried to keep John's Beatles history away from him, and played down being a millionaire pop star. It was only when Sean saw Yellow Submarine for the first time while at a sleepover at a friend's house that Sean recognized his dad in the film, and thus his role in the Beatles.
Tear Jerker: The "Eleanor Rigby" sequence manages to make the song even sadder and more depressing than it already was, which is no mean feat.
The clock in the Yellow Submarine speeds up to the year 2009, which only half of the band (Paul and Ringo) would live to see.
What Do You Mean, It Wasn't Made on Drugs?: In his book Up Periscope Yellow, Al Brodax, the man behind the production, who wrote or co-wrote most of the non-musical sequences, swears the only time he ever had drugs was in a meeting with John Lennon after he'd finished the script.
In the behind-the-scenes portions of the DVD, it's revealed that while the animators never did drugs, they would often return to work a little drunk after having a few too many pints during their lunch break.