The central reason that Faulkner chooses to narrate this tale in this way is to examine the downfall of the Compson family through as many different perspectives as possible. What is so interesting in this novel is that we do not get just one point of view. Normally in a novel, we either have an omniscient narrator or we see the action through the eyes of a first-person narrator. This novel presents us with the point of view of all of the major characters involved. This adds a level of depth and richness to the action that greatly adds to our understanding of the Compson family and what led to the downfall of the characters.
Of course, the negative side of this mult-layered method of narration is that it can be incredibly difficult and complex to follow such a narrative method. This is clearly shown through the way in which the shift in point of view and the information that characters share may often be in conflict with each other. Yet, in a sense, this only adds to the realism, as is shows the way that characters can experience one event and interpret it in many different ways because of their own individual perspective.