They bridge UI and UX — They ensure what the user sees (UI) translates into a smooth, logical experience (UX). Every visual decision has a usability consequence, and heuristics keep both aligned. They reduce cognitive load — Principles like Consistency and Standards and Recognition Rather Than Recall make interfaces feel familiar and intuitive, so users spend less time figuring out how things work. They humanise design — Rules like User Control and Freedom and Error Prevention remind designers that real people make mistakes and need a way out. That empathy is what separates functional design from great design. They give teams a shared language — Instead of "this feels off," you can say "this violates system visibility" — making feedback specific, objective, and actionable. They apply at every stage — Wireframe, prototype, or live product — these principles are a reliable constant throughout the entire design process.