TouchWiz was infamous for RAM management issues. Xposed allowed to operate in "Boost Mode," forcing hibernation of system apps that Samsung wouldn't let you touch. This turned a bloated Galaxy S4 or S5 into a lean, mean machine.
Here’s a text that “looks at” and Xposed Framework from a technical, nostalgic, and practical angle: samsung touchwiz rom xposed framework
TouchWiz ROMs were sensitive to hooking errors. A common issue was the "SystemUI crash loop" immediately after boot. TouchWiz was infamous for RAM management issues
For TouchWiz users, this was a miracle. TouchWiz ROMs were notoriously difficult to decompile and recompile due to Samsung's custom smali code. Xposed bypassed that entirely. samsung touchwiz rom xposed framework