I guess you will get more downloads, so that's potentialy more happy people willing to drop some $ if your stuff is good. And because it is humble to offer free that may be rewarded generously by big fans of your work who are financially blessed.
That's what I've seen so far with my free stuff. It seems like people will download the pack, see that it's good, and then go back and donate if they liked the art. It's not a bad system in my opinion
