Anchor lashings are used in order to avoid the anchors being lost while underway at sea. It should be noted that if the entire cable pays out in very deep water, chances are that the windlass would not have sufficient power to raise the combined weight of the anchor and cable. To prevent this, anchors are secured by applying the windlass brake, applying the guillotine and using anchor lashings. The anchor lashings form part of the securing system and are not designed to hold the whole weight of the anchor.
Source UK P&I