I learned how to negotiate pay for a new job(rule #1 - just do it!), how to navigate career and family, and a lot about how to present myself at work (eg don't use the word "just") for maximum benefit.
That's really only the tip of the iceberg but has probably made the biggest impact on me financially.
I didn't learn this here, but it is MM related and I will share since it was news to me. You can negotiate the price of a pre-construction home. I always thought the price was the price. This served us well in our latest home purchase.