Early in the Dragon Ball series, Goku and Krillin rescue a chick named Launch who could switch personalities by sneezing. What happened to her? They don't give any mention about her in Dragon Ball Z or GT, and she seems to have just disappeared in Dragon Ball.
According to the DragonBall wikia and TvTropes, Akira Toriyama gave a statement saying that the reason Lunch stopped appearing during Dragon Ball Z was because he simply forgot about her and that her bad state would have caused confusion because of its similarity to the Super Saiyan transformation.
She does appear three times in Dragonball Z's anime - most prominently at the beginning of the Vegeta Saga - although she mainly appears in filler or flashbacks. In the manga she doesn't seem to be there at all.
The original source of the interview seemingly in the March 24th 2013 edition of Mandō Kobayashi.