Pinning fixes an object as a snap reference. Pinned objects create virtual lines and points that other objects snap to when you drag them. Hover over an object (about 1 second) to pin it; press Escape to clear pins.

Pin up to 2 lights to align others. You get horizontal/vertical lines through each, and with two pinned: a through-line, midpoint, and perpendiculars.

Pin 1 wall to get a center-line along the wall and perpendiculars at each end. Use when drawing or aligning to wall geometry.

Pin 1 piece of furniture to extend its edges as infinite lines. Snap another piece to those lines to align edges (e.g. sofa and table).