When I was starting on my novel a few years ago, my first inclination was to use multiple viewpoints. Two drafts existed this way, moving between a set of five characters. Eventually, I locked in to one character, but how does a writer know when a novel should have multiple or single viewpoint(s)?
Beginning writers are more likely to fall into multiple POV. In my opinion, multiple POV allows a budding writer to get to know their own characters when they start a first draft. You write how Bob sees the world, and how Alice sees Bob, and what Chris likes for breakfast in the morning, and you know that Jennifer hates her job and why.
It's the "why" that writers are striving for. If you start a first draft, staying strictly with Bob, then you might not feel as close to Jennifer as you do with your main character. Sure, Jennifer will have her purpose (hopefully) within the narrative, but there is something binding about writing in a character's POV, a relationship that's created when you delve into the mind of someone else. But once that relationship is established, some writers don't want to let go. If they've given Jennifer a mind of her own, can they lock her out in another draft? It seems slightly unfair to Jennifer, doesn't it? But if you feel that guilt, you've done a good job of connecting with your character. You care about them. And because you care, you'll be better able to express who they are without giving them a viewpoint. It will come through their action and dialogue.
Imagine a first draft as the foundation for your final draft. That foundation is a playground - nothing's built yet - and your characters are your children being taken out for a day of fun. You let your kids out of the mini-van and they play, interact, throw some rocks, make some sand castles...all the while you (the parent and writer) observe each one of them and take mental notes. You see that Bob makes his sand castles very tall because he wants to emulate his father the architect, and that Jennifer loves to throw rocks because she imagines herself a princess fighting off trolls, and Alice sits in the corner by herself because she thinks no one likes her, and Chris starts digging a hole in the sand-box because he's trying to reach China.
You know your characters now - their goals, their mindset. The next step is figuring out a) what the story is, and b) whether or not you're going to let all four of your children in on it.
Some writers might presume that knowing their characters is enough to warrant a POV. But the question that should be asked is do you need to know the intentions of Bob, Alice, Jennifer, and Chris all-at-once? Even if Bob seems to bring something unique to the story that Alice doesn't, does that mean he should get his own take on the story?
Viewpoint is a story-choice, it's not the story itself. Even if you have four viewpoints, it doesn't mean that the four children are going to be interesting. It's the story that needs to be interesting in itself. And the story needs focus. Once your story has a purpose, you can choose a character (or characters) that best serve that purpose. But remember - there should be a reason that Alice and Bob both get a POV. If Alice pops in for one scene to say her piece, you need to know that there's no other way to let the reader know who she is. Can she tell Bob? Can she show Bob who she is by her action? Do we need to know exactly what she's thinking in that one scene?
Multiple POV can be an easy route. A writer doesn't have to work as hard to show a character through action when they can open up that character's mind and tell all. Even in third person, the thoughts are there, told through a narrator.
I'm not downing the use of multiple POV, as long as it works, but in many cases it's not needed to serve the ultimate goal of the story. A lot of the time it detracts from the intrigue of the novel because the writer takes up pages letting each character have their say without moving the story forward at the same time. We see one event happen in the eyes of three different people. That repetition slows the narrative.
I would recommend the use of multiple viewpoints for a first draft, only for the purpose of getting to know your characters. That will give an idea of who is going to be the most compelling viewpoint, and more importantly, who is going to drive the story forward. If you decide to add another viewpoint, even for a chapter or two, you will at least have a sense of that character and their purpose, and knowing that purpose will keep their viewpoint focused and necessary. It will aid the story - not detract from it.
So, if one of Jennifer's imaginary trolls comes to life, kidnaps Alice, and escapes down the hole Chris has been digging, your story has begun - but who to tell it? I'm voting for the kidnapped Alice, the loner who finds her true self as she escapes from an evil troll kingdom. But maybe Chris' daring bid to save Alice could provide more adventure. That's ultimately a writer's choice, and a very important one.