The OBJ Export Options window is displayed when you save a model in OBJ format. It allows you to specify things like whether or not to save the normals in the file and what level of precision you want (which affects overall file size).
The Save Normals checkbox allows you indicate if you want the normals saved in the file or not.
The Vertex Decimal Places input box allows you specify the precision of the vertex coordinates. The number shown indicates how many numbers will follow after the decimal point.
The Texture Decimal Places input box allows you specify the precision of the texture coordinates. The number shown indicates how many numbers will follow after the decimal point.
The Normal Decimal Places input box allows you specify the precision of the triangle normals. The number shown indicates how many numbers will follow after the decimal point.
Click Ok to save the model with the specified options or click Cancel to ignore any changes.