Regarding the use of stream-of-consciouness, the posts above do a good job of discussing how this technique lends itself to a unique and powerful intimacy with the narrators in the novel as well as a complex, highly psychological type of exposition wherein we see that interpretation of event is as important (if not more important) than an event itself.
Another element of Faulkner's narrative modes in this novel relates to the notion that different periods of time can be explored through the various narrators. With each new narrator, we experience and gain access to a different historical moment in the life of the Compson family. Switching narrators lets us view these different moments through new lenses as well.
I must admit when I first read this book I was amazed at Faulkner's incredible use of point of view and how he merges the point of view of many different characters to gradually reveal the truth of what is going on and has gone on in the lives of the different characters involved in this funeral trek. What Faulkner is famed for is his use of the stream of consciousness narrative, as #2 points out, and this novel is an excellent example of how this is used in a unique and highly creative way.
The use of different narrators in Faulkner's seminal work is intriguing, if not rather frustrating. No reader forgets his/her first efforts to decipher the narration as told by Benjy, a severely mentally disabled man of thirty-two. His recollections are convoluted, moving backward and forward with memories mixed with impressions. Even critics do not exactly know what to make of this point of view.
The most famous narrative mode used by Faulkner is stream of consciousness. Some people love it, and some people hate it. The idea is that you see less punctuation and there is no filter between the narrator and the reader. It makes you feel like you are there, where the action is, but it can be difficult for the reader. I enjoy stream of consciousness, but I admit it wears me out as a reader!