[The Saucepan Man]

As I understand it, the main purpose of Sauron's attack on Erebor was to forge a way through the northern passes to Rivendell. And what prizes Rivendell and Lothlorien would have been to Sauron. Quite apart from his own satisfaction at capturing these Elven strongholds, their fall would have had a very serious effect on the morale of those who still held out. So I can certainly see why Sauron was keen to attack these strongholds.

Even if he would have been unable to conquer them without first recovering the Ring and perhaps directing the attacks himself, he could at least prevent their occupants coming to the aid of Gondor. Perhaps he was also hoping to prevent the remaining Elves making their way to the Grey Havens before he was strong enough to defeat them. For this reason, I agree with the point made by Lost One that he would have used the Corsairs to attack the Grey Havens had Aragorn not defeated them at Pelargir.

I also agree with those who have said that Sauron had no concerns about over-committing himself militarily. He had more than sufficient forces at his disposal to achieve his military aims. One point does occur to me, though. As I understand it, Sauron needed to exercise his own will to direct his armies (hence they scattered when he was destroyed). So perhaps the fact that he committed his armies so heavily across Middle-earth contributed to his fatal mistake in overlooking the approach of two little fellows with a Ring.