The all-knowing, all-seeing, third-person omniscient point of view (POV) is the most common literary device that writers use to tell a story. This gives an author the opportunity to shift points of view among a number of different characters. But some writers may choose to use a first-person POV, which is more restrictive and limiting than third-person, but also offers advantages, such as placing the reader directly into the mind of the main character.
Advantages: Direct Access and Urgency
One of the primary advantages of the first person POV is that a reader is given direct access into the mind of the main protagonist. Knowing every thought that precedes a character's action helps a reader identify with the choices the character makes. The first-person POV technique also helps create urgency in a story because readers only know as much as the POV character does, so each discovery or revelation is a surprise. This is especially effective in mystery stories and thrillers, in which the unraveling of conspiracies is a key element of the plot.
Advantage: Character Building
Another advantage offered by first-person POV is character building. By writing from inside one character's mind, a writer maybe be able to develop a fuller and more complex protagonist. First-person POV characters tend to reveal themselves more through their words, rationales and excuses than third-person POV characters who are often written from a more distant perspective. First-person POV also allows writers to employ literary techniques, such as flashback, without interrupting the flow of the story.
Disadvantage: Limited Perspective
One of the disadvantages of first-person POV is the fact that readers are confined to one perspective for the entire story. No matter how well a protagonist is written, there may come a time when readers feel claustrophobic because they are trapped in one person's mind for too long. This can also lead to a feeling that the narrator of the story is unreliable, because there is no other perspective to measure against what she is saying in the story. But there are instances, however, in which an unreliable narrator is an intentional device a writer uses. For example, in a mystery or thriller, a narrator may be pursuing a killer, and provide facts that later are shown to be false, because the narrator is in fact the killer and was hiding the truth.
Disadvantage: Lack of Subplots
In third-person POV, a writer can create multiple subplots using different characters to generate story lines. But another disadvantage of first-person POV is that it's very difficult to develop subplots without putting the main character into each one, which isn't feasible. Subplots give scope to a book and provide more layers for a writer to tell her story. They can also increase tension because a writer can switch from a cliffhanger scene in the main storyline to a subplot and leave readers on the edge of their seats.