The bottom line is knowing the type of home, room, patio or porch you have will enable you to narrow the choices and choose the perfect door system. You‘ll also need to consider the climate where the doors will be installed. This will dictate material selection, how the door is hung and the style suitable for that particular application.
On a more practical level most home owners want to control light, dark and other features while extending the living space. Additionally, a homeowner may use sliding closet doors with mirrors to make the inside a room appear larger or create perceptions to control the ambiance of the space.
Most of the time when you seek out a door, you will see many of the same things. Not necessarily that all doors are the same, but rather you will see many of the same styles. While doors even within styles are technically different, they still retain the overall feel of the style. If you want a truly unique door, you may have to think outside of styles and even outside of the box.