The introduction of Buu was held back to allow Toriyama to explore a "slice of life" story with Goku's son Gohan, which ended up having an even bigger impact.
Before Akira Toriyama's Dragon Ball became a hit, he received plenty of rejection. But some of those rejected ideas found their way into Dragon Ball history.
Eiichiro Oda revealed that the only way he is able to continue to come up with story ideas is to push himself as far as he's pushed the Straw Hats themselves.