If you haven't signed up, you can do it online or in the store. Basically, certain products will give you points, which turn into credit you can spend at Walgreens. (See their "fine print" for exclusions.) See the chart above for point values. (Currently, you can still earn Register Rewards for some items. That is totally separate from this program and does not affect point redemption or earning points.)
The "fine print" doesn't cover everything below, but it's what I've learned along the way.
You can purchase as many items as you want and the points will multiply. (They do have the right to limit you.) So, if Product A gets you 1,000 points, buying three of Product A will get you 3,000 points. There's no need for multiple transactions. They have changed this. Each deal has a limit of one reward per transaction. You will want to do multiple transactions, if you want to maximize your points.
2) You will get store credit if you need to return an item you "paid" for with points.
3) You will not earn points for a product that you normally would, if you are redeeming points or using store credit. (I suggest paying for items that generate points in an separate transaction.)
4) You cannot redeem partial points from the chart above. I attempted to spend 59¢ after earning 5,000 points. The cashier was not given the option to break it up. I could have used it, but I would have lost the remaining $4.41 value.
5) You can get a raincheck for the sale price, but you will not earn points when you redeem the raincheck.
In my opinion, the major flaw of Balance Rewards is the redemption. You can't redeem part of a reward or earn new points when you're using your existing points. I'm assuming you can drop down a tier if you have hit a higher redemption amount and want to redeem less, but you will always have to hit at least $5. You also won't want any part of that $5 to be on an item that would earn points since you will forfeit getting new points.
I don't see myself getting into this since I normally buy only the super deals at Walgreens. I'm assuming that the "super deals" will soon be only the Balance Rewards items. If I want to redeem points, I won't earn points — making a potential great deal not so great anymore.