Circulation is the walking path from a door to a room's key destinations — a sofa, a window, another door. A good plan keeps that path unbroken even after all the furniture is in.
A common rule of thumb is at least 90cm of clearance on a primary path, and 45–60cm minimum where a secondary path squeezes between furniture. The path should never cut straight through the middle of a piece of furniture — it should flow along its edge instead. Facing a sofa's back toward the path is itself a signal that "this is where people walk."
Placing furniture before drawing the path is how a sofa ends up blocking the only way through, discovered too late. Drawing the actual footsteps as arrows on the floor plan first, then placing furniture around them, is the safer order.
When to use
Before placing furniture, sketch the path from the door to each key destination as an arrow. After placing furniture, walking it in person is still the most reliable check.