Narrative Structure - How many Points of View?

Tonight I'm off into Leicester to give the third class in a series of five on "Starting to Write a Novel". The classes are organised by Writing School Leicester, and I am much enjoying them. After half-term, I will be giving another series of classes there, also on novel writing.

I've just finished writing a page of notes on the subjects I hope to cover tonight. And this has got me thinking about narrative structure - particularly about the number of points of view (POV) included in a novel.

The simplest case is a novel with a single POV. This could be a first person story or a third person story. Either way we would see the story through the eyes of one character from start to finish. The second option is a story where we see through more than one character's POV. One chapter might be in one POV the next chapter a different POV, and so on.

Some kinds of thriller would be hard to narrate through a single POV. You might want to swap between a warship in the Atlantic, an agent in Berlin and a military advisor in London, for example. And perhaps many more.

My question is, do we lose anything through swapping POV in this way? If we were to have half a dozen POV characters, would we lose the intimacy offered by a single character, followed through the story from start to finish?