You don't really save much. We got tickets to Le Reve and saved about $30 for two tickets. Sometimes if you buy in advance you can actually get better deals online.
Here is how it works:
1. You go to the booth 30 minutes before it opens.
2. Stay in the line while you're watching their scrolling tv and see if you see a show that you like. Don't be surprised if you don't see the show that you are looking for. When we went there they didn't have the Cirque Du Soleil O show but they did have David Copperfield at 40%-50% off.
3. When the door opens, go inside and buy your tickets.
4. !important! Go to the box office at the hotel right away and get your actual tickets with seat assignments. You can do that 1 hour before the show but we went right away.
This place is great if you don't have a plan for the night and want to find something to do, just drop by and you can get really good deals on certain shows, just don't expect 50 percent off tier 1 shows.