Why did Gandalf save Faramir?

Originally Posted by hewhoarisesinmight

In the Return of the King Gandalf himself that by him saving Farimir many more would die on the Pelennor. Why did he do it then? Did he think the life of Farimir was worth more then the all the 'commoners' that Gandalf could have saved? Its not like that saving Farimir would have helped with the War of the Ring Farimir did nothing to help that after he was almost killed by his father.

On a personal level, I totally understand that, after what Faramir wen through, he didn't really have the energy to fend for his kingdom-thing. [I'm not really sure what the correct terminology is.] Honestly, I think he might have just wanted to let Aragorn to take over... IDK.