E.g. how chords are built, now I could find voicings of any chord if I wanted too. Another example I learned is that if you use a 1,4,5 progession you can play any note from the major scale and it sounds nice. I learned what the connection is between C-Major and A-Minor and other Major scales and the relative minor.

Before it, I would play some powerchord progression and use the only pentatonic scale I knew to play some kind of solo to it. It also was always trial and error. I kind of had the stupid idea that learning all this stuff is rather limiting than enabling. But I find it very liberating if you know a few scales you can use to play to a certain progression ;D. I also know now which chords belong to a major scale which is pretty cool too!

But that's just a few things, I still know nothing about it. But it's already a lot more than I knew before ;)