According to USA Today on Dec. 3, Peter Jackson indeed thought that Benedict Cumberbatch highly qualified as the voice of Smaug in "The Hobbit: The Desolation of Smaug". In fact, Jackson thought that "Smaug has to be more than just a voice".
The director also thought that there had to be presence of high intelligence to the point where the dragon seemed even smarter than Bilbo. Jackson joked, "I'm not saying Benedict is smarter than Martin, of course".
Jackson figure that Cumberbatch had such a sharp mind and voice that he had emitted a rather scary presence to the role. Though last year "the Baggins" could pretty much figure out Gollum through a battle of wits, but this time, Smaug would be considered a rather formidable foe.
"With Smaug we wanted to keep it much more unpredictable. So literally, we wanted somebody scary. He's like the Hannibal Lecter of the dragon world".
According to Jackson, Cumberbatch was able to immerse himself into the role of Smaug in quite an unusual fashion.
"He stripped off and rolled around on a sheepskin rug. I'm not exaggerating!"
One might be scracthing their head trying to figure out why Cumberbatch would do such a thing, but one may think that this may be analogous to Smaug maneuvering through the mountains of gold in Erebor under Lonely Mountain.