You should always keep the load wires closest to where you will be using, or integrating, the light source. So if you’re going to be integrating your light bulbs in a lampshade, line wires are used and vice versa.
The big difference is how they work. Load wires use voltage transformers or dimmers to change the device’s power consumption and intensity of output. Line wire fixtures require more wattage than load wire fixtures and do not contain any transformers within their construction as they are designed for installed lamps or stationary posts that do not require altering their electrical properties with a dimmer switch or transformer in order to reduce power from them when necessary. Load wires can turn on quickly while line wiring takes much longer for electricity to activate.
Load wire fixtures are also typically more versatile than line wire fixtures, for example being able to be dimmed or set to different colors.
Overall, load wire fixtures are appropriate for illuminating areas where line wiring isn’t feasible. That includes individual lamps in a room where you want to control the specific brightness of each bulb. Line wires are used for decorative lighting where dimming isn’t necessary, say under cabinet lights in a kitchen or outdoor lighting on a deck.
