Pitch-modulated collision sounds (scraping, tire skids etc.) depending by the speed of the collision. For example, tire skids at high speeds to have an high pitch compared to skids at slow speeds.
Parent-child feature in editor, when putting an object under another (not move up or down in list, just into parent object in hierarchy). For example, a pop up light mechanism, which has multiple different parts doing different things when opening. Parent will rotate and rotate the child object under it too, while child object is rotating or moving elsewhere. It could unlock more possibilities about pop ups or other mechanisms.