A line set groups multiple connected segments into a single editable object, allowing designers to manipulate contours

http://janequotes.byz.org/index.php?title=HVAC_Line_Set_Planning_for_Single-Zone_vs_Multi-Zone_Systems

A line set groups multiple connected segments into a single editable object, allowing designers to manipulate contours, outlines, and paths with consistent thickness, style, and snapping behavior across a project.