This is especially crucial in order to enjoy a fictitious universe with numerous authors. For example fans of the Star Trek shared universe may choose to reject any episode that does not fit in with their view of said universe. This is not to say that the viewer denies the episode's existence, but rather mentally sets aside any facts stated in the episode. A prime example is the Star Trek animated series, which many viewers chose to ignore.
Another example of this would be the Highlander movie franchise. Many people chose to ignore the second movie because it turned everything laid out in the first movie on its ear, more or less just to make a quick buck. The makers of the third Highlander movie practiced their own form of Krypto-Revisionism and continued the franchise in the vein of the first movie, choosing to disregard the whole plot of Highlander 2.
wikipedia.org dumped 2003-03-17 with terodump