The Mesh UV projection uses the Mesh's UV coordinates to map the Texture to the surface. This is the default behavior for all TexturesTextures are used to add details to a surface. Textures can be procedural or imported raster files., so in many cases, it's unnecessary to use a Projection node when mapping a Texture based on UVs.
Figure 1: Using the Mesh UV Projection node to extract a UV set from the object on which the material is applied
This Projection applies a spherical mapping for Environment textures and IESAn IES light is the lighting information representing the real-world lighting values for specific light fixtures. For more information, visit http://www.ies.org/lighting/. light distributions. For more control over the Projection (mainly rotation), use the Spherical projection.