Stacking modes

Mode Usage scenario
Stitching (Panorama) Combine multiple images to a panorama
Average (Noise-Reduction) Averages the pixel values of all images, can be used to reduce noise or to simulate long-exposures
Median (Remove Objects) Uses the median value of each pixel across images, can be used to remove moving objects, but usually needs at least 5 images
Maximum Uses the highest pixel values of all images, can be used for star-trails
Minimum Uses the lowest pixel values of all images
Add (Bright images) Adds all the pixel values of all images, can make a lot of underexposed images brighter
Light-Compression (HDR) Compresses the lights and shadows of all images. Useful if you have an exposure bracketing and want to generate a HDR-Image