This option adds a polygon to the FACT's UV space that can be used as a placement guide.

The UV spaces of individual groups within an OBJ often all refer to the same defined texture. This enables you to texture multiple groups with only one texture. However, the information about the "border" of this texturemap is not stored in the OBJ file. If you directly convert the UV space of the OBJ to the UV space of the FACT, it will have no border and will "float" in space.

If you try to use the autoalign features in EI to align the texture to this "floating" UV space, it will be scaled to the dimensions of this floating portion. It can be very hard and time-consuming to align the much bigger texture to only this portion.

Make Texture polygon will give you the border of the UV space. Now you can use the "align to front" or "alingn to polygon" option in EI to place the texture exactly where you want it with a single click.