if everything is done correctly with good form and relaxed... you will increase strength, balance, flexibility, and also get some nice abs (I eat a lot of pasta and stuff, and my abs still showed from that class). When I took that class 2 years ago at my college, everyone was saying I lost some weight and had a good stomach even though I was in good shape and was not overweight at all. I am taking it again this fall semester because I want to get stronger in the core again, and get my abs to show. That class is also when I realized about trigger points and the big painful knotts I had in my piriformis when we were rolling with the massage balls and foam roller. no more pain in my hip abductors, still little ache here and there in my piriformis/hip flexor that comes back every now and then and same with between my shoulder blades, but that is about it. My pilates teacher after the 2nd day of class recommended me to go to the chiropractor she goes to and told me she recommends it to all her students that has posture problems and pain to go to because I had poor posture and had trouble doing a lot of the movements (like she was talking about me not sitting on my sit bone, one hip/shoulder higher than the other, etc..and she was right..I also had back pain and neck pain too). then I saw the chiro and then all the pain was gone, and I was able to do most of the movements in the class (went once a week for the 1st 2 weeks, then once a month til I figured out how to keep everything in alignment, now every now and then when I need to)
I still have trouble trying to do sit ups and jack nives though, soo hard. I cant get my back off the ground and I still cant. The exercises that required that, I had to do modifications. Everything else I could do fine. I also liked the reformer.
Note: just because I saw a chiropractor and he helped me, doesnt mean it will help you unless you can find a good ones. My pilates teacher has been to a bunch of chiropractors before she found the right one that knew what he/she was doing, the one she has been going to and recommended to me and a lot of her students. This guy also helped heal my ankle sprain last year (I waited 1 week after the sprain to see if it would heal and I had to wear an ankle brace playing sports or it would be really tender and hurt), I was back to my activities right after the adjustment (had to re-strengthen my ankle to be strong and it is stronger than ever before now, no sprains since). I am just letting you guys know this because not all chiropractors are the same and it is hard to find the right one. The right one heals you at least 75% in 1 session or heal you fully depending on what is going on with you and does not want you to keep coming or wants your money (wants you to heal).
Pilates requires good posture. You won't get hurt if you do everything correctly and if nothing is holding you back. This is my experience with pilates and it helped my posture big time and being aware of how I move and things. I hope you enjoy it, good for your core if done right.