@Lord WyrmSpawN
Characters learn lessons intentionally or unintentionally from Discord’s chaotic/trolling actions or he learns something himself and improves.
In terms of helping intentionally or otherwise:
Twilight learned a lesson in s4 premiere.
Twilight learned a lesson in jealousy
He help unlock the chest and get the mane six to know they needed to.
Got the reformed squad to chrysalis hideout, distracted the changelings
Unintentionally taught big Mac and sugar belle a lesson in love. Intentionally got them back together
Made it so twilight wasn’t being forced into a position she wasn’t ready for yet and ultimately helped twilight be a confident and prepared ruler of Equestria in a roundabout way.
In comics helped saved an entire kingdom, defeated cosmos.
In g5 sunny has learned a lesson and the mane five are gonna put even more of their all into building a better equestria with harmony.