"Importance" greatly depends on your desired outcome. If your goal is for the sample to sound natural, you likely won't want to stray more than three semitones from its starting pitch. This is unless you are also changing the timing of the sample.  That said, pushing samples beyond conventional limits can result in interesting and unique sounds. "chip monking" vocals (where you pitch them WAY up) are very popular in some modern genres such as Hyperpop.  Additionally, vocals pitched down to extreme degrees can make the singer sound like a monster, a technique often used by somber pop acts like Billie Eilish.