Projection nodes can add or edit existing UV mapping coordinates of a texture map. These nodes do not alter the actual 3D model's UV coordinates - they simply apply a new UV projection to its connected texture. Most likely the Projection settings are most often used for texturing objects, but can also be used for other purposes, i.e. for adjusting HDRIAn image which presents more than 8 bit per color channel unlike most common image formats. background images, such as rotating.
← UV Projection
The image below shows the Projection orderly set to Box, Cylindrical, Perspective and XYZZ to UVW.
