The TKTS booth is a great way to get discount tickets for many shows. I live out of state (in Ohio) and whenever we come into the city, we buy our tickets through TKTS. If you do your research beforehand it's a great way to see more shows for less money. First off, find a site that will tell you what is on the boards each day. I use
https://www.entertainment-link.com/tkts.asp which gives you a day by day listing of what is on and how much off you get. Keeping track of the grosses is also a great way to figure out which shows will be available. Next, as the trip nears, see what seats are available at each of the shows you are seeing, every day you'll be there. Keep note of which shows have better seats availble on certain days. For instance, I did this before my trip so I knew that I had a better chance of getting tickets to see Curtains on Wednesday evening than the matinee, and Les Mis was the other way around. This allows you to get the most bang for your buck.
Since the South Street Seaport location opens earlier, you can sometimes get better tickets to see shows. It also saves you time if you want to see both an evening show and a matinee. The lines here are considerably shorter, but they also have less windows open. We waited around 30 minutes at the TKTS there and around an hour at the TKTS in Times Square. That's an average of showing up when the booth opens. I'm sure it changes based on when you go though.
The boards are easy to read. If the show isn't on the board, it isn't available. A lot of times all the shows will not fit on the screen, so the board will flip back and forth between the two sets. You'll find out what seats are the best available at the counter when purchasing. Remember to pay in cash or traveller's checks, or else you can not buy tickets through the TKTS.
Hope I helped and Good Luck!
"A bird doesn't sing because it has an answer, it sings because it has a song." -- Maya Angelou