Like what meaning and reasoning
Why it is "Too late" for Vader when Luke is trying to get him from the Dark Side.
The relationship between Obi and Vader.
Back story of the Jedi and why Obi and Yoda are the last ones and in hiding. Also get to know about the Sith
The relationship between Palpatine and Vader.
How Palpatine came into power, and why a war is going.
Why Vader was the one that ended up balancing out the Force.
Why certain people are Force sensitive
Also it did a lot of world building definitely when you add in The Clone Wars.
Ignoring The Prequels Trilogy, you are throwing away TONS of potential storytelling. Only but so much was brought to the table with the Original Trilogy.
You got to take it all in as a whole to get the full impact, IMO. Gonna peep out the PT novels because they supposedly do a better job at telling the story for that arc.