Villains have all the issues of multi-character POV -- dramatic irony vs. identification, and how it affects the formidabilty of characters -- but they give them their own twist.
Any good multi-POV story will have dramatic irony. Switching POV is a way of conveying information, if only the POV character's reactions, that the previous POV character didn't have. But the villain's information is drastic in this way. Providing that the hero doesn't know it already, somehow (monologuing, anyone?), his lack of information is often crucial in the plot; he has to not only stop the villain but deduce how to stop him, and ignorance of what the villain is up to can seriously complicate that. Then, by the same token, it will mean the reader knows more than the hero about his precise predicament.
And seeing a character from his own POV affects his characterization. Some are more impressive without such views -- Sherlock Holmes, Jeeves. Some are more impressive with it -- Walter Mitty. But Walter Mitty would not make a good villain. Villains who can't act don't make good obstacles. And the more of an impression they make, the harder it will look for the hero -- even if it produces no change in his real task.
OTOH, to make the villain's motivations clear, and make him more sympathetic, his POV can be useful. Sometimes it can be essential, if he can't be counted on to tell the truth, and there are no other sources. But, on the third hand, knowing his motives can distract from the unquestionable extent of his acts without skillful handling.
Minions can be useful in this regard. Not being the top man, they do not know everything, but they still can have a clear sight into what he is up to and sometimes even why.
Minor villainous factions can be handled more easily. The snipping, back-biting courtiers who resent that a mere scholar of magic can deal with the king do not have to be too impressive. Indeed, they may need not to be, so they can be destroyed or subsumed before said scholar has to take on the evil warlock that's rousing the dragon that lives under the city. Their evil can be brought out with their pettiness, their envy, their self-deluding excuses for hating the hero, which keeps them from having to complicate the main plot too much.
Then, sometimes they don't know enough. . . .
