What are the advantages and disadvantages of 3D movies?

Our ability to see in 3D comes from our "binocular vision"

Because our eyes are a small distance apart, they each see a slightly different image. Our brain can take these two images and use the small differences between them to give us our perception of "depth", which is the basis of 3D vision.

Because normal movies are presented on a flat screen, this is not possible.

However, you will notice that 3D glasses have two different coloured lenses. This means that, when wearing the glasses and watching a "3D" movie, our eyes are once again seeing slightly different images, fooling our brain into thinking we are seeing in 3D.