Long exposures can be a lot of fun when you are shooting a landscape. They allow for a few different effects which are really useful. The first is motion blur, in which you can make the sky or a flowing water source appear like a smooth ribbon across your image. It can even make the stars into white lines which move across the sky, or turn moving people and vehicles into blurs of colour and light. The second is to allow more light into the sensor, which means you can capture a clearer image even when there is not much light to speak of.