Talking from a very personal perspective, I believe it [Open Class] made a big difference along my journey because it gave me the environment I needed for practising. If you want to settle what you learned in class, having a concept like this is key.
Socials, even though you learn a lot, are different - everything goes fast and you just go for the fun. However, I always used open classes for working on technique and get a transition from "the theory learned in class" towards "the practise". It is not the same learning a new move isolated than in an improvised dance sequence, you need to work on "greasing" the whole thing to make it look smooth. And many times, the key relies on a small detail that only a teacher's eye can catch, and this makes a huge difference... it is like somewhat which helps you to unlock a figure completely.
