One of the annoyances of digital cameras with interchangeable lenses is dust on the sensor. The sensor can be like a magnet for dust when changing lenses and it needs to be cleaned from time to time. Some modern cameras have built in technology to avoid dust on the sensor but many cameras don’t (like my Canon 5D). This dust can then appear on the finished picture as a very distracting spots and is especially visible on clean areas in the frame like blue skies.
As spots on sensor are pretty common one of the most requested features of Lightroom in the beta program was a feature to remove spots and blemishes. It came as a late addition to the program in the form of the clone/spot and healing tool. It can be found in the Develop module (accessed in the toolbar below the image or by pressing N key). With this feature it is easy to remove spots by selecting an affected area and it is replaced by a sample from another area. The difference between spot and healing is (taken from the Lightroom manual):
Clone: Applies the sampled area of the photo to the selected area.
Heal: Matches the texture, lighting, and shading of the sampled area to the selected area.
When clone/tool has been selected the mouse pointer changes into a circle to select the area to fix - it is very convenient to use the mouse scroll wheel (if available) to control the size of the circle. When the area has been clicked a sample area is automatically selected which can afterwards be dragged to select another sample area. It is also possible to select an area to fix and click and drag to a sample to area to be sampled. The size and location of each fix and sample area can easily be changed afterwards with the mouse. It is very useful to press and hold the H key to hide other fix areas when selecting a spot (useful when many areas of the picture have been fixed).
As the spots are in the same location in the frame for a photo session the spot and healing settings for a picture can be pasted into other picture like other adjustments which is very convenient.