When you're considering repainting, knowing the LRV of your current paint color can help you better predict whether a new prospective paint color will bounce back more or less light than your current paint color. It also gives you another data point to assess when you're comparing two paint colors. (Pictured above: "Revere Pewter" HC-172 by Benjamin Moore.)
Some factors that can limit the amount of natural light in your home include: a heavily wooded lot, windows covered by a front porch, windows covered by a screened porch, close proximity to neighboring buildings, and north-facing windows.
In spaces where natural light is limited, selecting a paint color with a higher LRV can maximize the available natural and artificial light (though of course, LRV is only one piece of the paint color selection puzzle, and a higher LRV paint color won't in and of itself make a dark room "feel better").
As discussed below, knowing the LRVs of prospective paint colors can also help you to create a cohesive paint color plan that flows from room to room. It's also important to note that contrary to popular belief, wall paint colors should not be the first selection that you make for a space, but instead should be chosen after you have selected the area rug, fabrics, and fixed elements such as countertops, cabinets, tile, and flooring.