It's been a whole two and a half weeks since I last complained. Today feels like a complaining kind of day. It's raining and cold, and I'm sick, and I have to go back to work tomorrow. Time off always passes too quickly.
For the sake of this post, I'm assuming the story is told in a third-person point of view.
A scene should be from the perspective of the character who has the most to lose in that scene. Barring that, the one upon whose shoulders the outcome lies, the one who makes a decision that turns the plot, or the one who sees the most of what's going on, can all serve as a good narrator.
However, when you hop from one character to the next, you're tearing the reader away from a previously established relationship to another. You're creating more work for yourself, because you need to create that emotional connection, a reason to keep reading, within each perspective. You have to get the reader invested in each perspective character. If you don't, you run the risk of the reader skipping past that section, or putting the book down entirely and not picking it back up. You can have the world's most compelling story, but, if the reader isn't emotionally invested, it's gone to waste.
The worst symptom of there being too many perspective characters is head-hopping. That's when, in the middle of a scene, you shift from one perspective to another, often without anything to mark the transition. It's jarring, and looks sloppy, like you weren't paying attention to who was telling the story.
I've read a lot of books with the above problems, and I've marked at least one star, sometimes more, off for it. It left me feeling disconnected from the narrative, and it felt like the author hadn't gotten his or her thoughts in order in the final draft.
When you're writing your story, initially, try to tell it in as few perspectives as you can. In later drafts, you can expand the perspectives and have each of those characters matter to the reader. But, when you're just getting the story down, it's a lot of work to add on top of plotting, characterization, theme, setting, and whatever else you're trying to include in your first draft. As you go through each reread, ask yourself if each perspective character adds enough to the narrative to risk disconnecting the reader from the story. If the answer is no, find another way to convey the information.
I can post about the various perspectives and how to decide which to use at a later date. For now, though, I'll be content if one future author takes it to heart that there's such a thing as too many perspectives.