Extending gear means clipping a long sling to a piece of protection (bolts or traditional pro), and it is a vital part of learning to lead, especially on long, blocky, or wandering routes. The top two reasons for extending a placement are minimizing rope drag and keeping the rope from levering out pieces (especially nuts) or causing cams to "walk."
Rope drag is caused by angles in the cord running between protection, or the rope passing around and against angular features in the rock. It can also result simply from climbing a very long pitch, even if the rope runs mostly straight. In bad cases, drag can make it difficult to pull up the rope to clip into protection, or even to move.
Clipping the rope to a nut or cam without extension can lead to the rope pulling a piece out of its original placement, rendering it useless, or even plucking the piece completely out of the rock.
Three Ways to Extend
Use a single- or double-length sling, depending on how far you need to extend.
Two or more quickdraws clipped together. Make sure to clip the second biner into the dogbone/ webbing of the first draw; don't clip the two biners together to avoid metal-on-metal contact.
Two or more nylon slings girth-hitched together for really long extensions.
Roofs: Extend a quickdraw underneath a roof to decrease abrasion. Similarly, extend placements to prevent the rope from pulling or rubbing over sharp edges of any kind. Example: A piece of protection directly above a knife edge on the second pitch of Yellow Spur (5.9) in Eldorado Canyon, Colorado, was improperly or inadequately extended. The leader took a fall and subsequent pendulum swing, which caused the rope to rub across the edge and sever. A sling on that piece would have been pulled straight down and over the edge, avoiding the drag across the edge by the rope and the runner, which is what caused the rope failure.
Traverses: Protection on either end of a traverse should be extended, especially if the route drastically changes directions before or after. Similarly, protection on either side of the main climbing line (versus a straightup crack) likely will need extension. This keeps the rope running straight and prevents that Z-shape that causes severe rope drag.
Ledges: Pay attention to where the biner will strike the rock if you take a fall, making sure the biner itself will not strike an edge directly, which could cause it to bend or break. Here, the clip is right above a 12-inch-deep ledge; extend the gear so the biner will not fall on the corner of the ledge.
Lowering: When lowering and leaving gear for a follower or another burn on the route, make sure to unclip any draws that pull the rope into the wall, causing it to run over a sharp edge.
Hard to Reach: Extend a draw or add a sling for redpointing if a clip is hard to reach.