Three years after painting, when you want to touch up a wall or repaint one room, “light grey” isn’t enough information. Different brands and even different batches can vary. Without exact details, you end up guessing, and often the new section doesn’t quite match the old.
Writing down the brand, shade name, number, and finish (matte, eggshell, satin, etc.) for each room—and keeping that in your home file—means future you can just reorder the right paint. Even if the store runs out, they can often mix the same formula again from the code.
It turns repainting from a puzzle into a simple repeat order.