I just started using the Millennium Falcon in Angry Birds Star Wars. After completing all the other levels with 3 gold stars, I had 75 Millennium Falcons.
I wasn't really sure how game play would work, but now I have a better idea. Once you select the Millennium Falcon, your current bird is changed into an egg. That egg, after being launched and coming to a stop, acts as a target for the Millennium Falcon, which flies in and release a barrage of shots. The Falcon always does substantial damage, making most levels fairly easy.
The Falcon attacks are strangely scored by percentage, rather than points. That makes it rather confusing, as it is unclear what makes a full 100%, or what prevented you from achieving that percentage. Also, you seem to get some kind of credit for having unused birds, but how much they count for is not clear. It is often a toss up between using the birds to attempt to reach 100%, or using an additional Falcon on the level.
Every single time you use a Falcon, one is deducted from your total. So if you retry a level multiple times, you will use up more of your reserve of Falcons. Also, if you kill all of the pigs, the level will end, and if you haven't reached 100% (if that is your goal) you will have to do the level over again, using additional Falcons. So in order to get 100% you may have to miss one of the pigs intentionally, to give your more opportunity to destroy the structures.
As I mentioned above I had 75 Falcon when I started the playing. I began with Tatooine, and thought I would easily clear all the levels and be able to try some Death Star levels. It turned out to not be the case. I used up 75 Falcons, only completing 31 levels, with two of them not reaching 100%. There is the option to buy more Falcons, but this seems rather unscrupulous (as it requires you to spend money to complete the game), as a lot of money would be required to complete all 140 levels (soon to be 160).