For hanging lights and other items. Currently there are a couple of chains or items with chains attached, but it's not always possible to sink into a wall, or hurts to use multiple slots when we're constantly fighting the limit. I'm sure I'm not the first to have thought about this, but here's a realistic proposal within the confines of current mechanics:

Since we have interactive items like lights, and now books, a chain could be made with an "interact" prompt that lengthens or shortens it a few times. Maybe 3 different lengths. Model-wise, since chains are typically just a couple of 2D planes, it should be trivial to hide the length by doubling those up until activation.