Samsung's TouchWiz was often seen as "over-designed". Xposed became the go-to solution for refining this experience. Popular reasons for using it on Samsung devices include:
Some popular Xposed modules for TouchWiz ROM include: samsung touchwiz rom xposed framework
Because the official Xposed didn't work, the community had to step in with specific "fixed" versions: Wanam Xposed Samsung's TouchWiz was often seen as "over-designed"