Both LightWave and Unity use "left-handed" coordinate systems but FBX is right-handed, which means LightWave has to convert to the right-handed coordinate system, and Unity has to convert from the FBX right-handed coordinate system back to its left-handed system. The way to convert from left to right-handed coordinate systems is to invert one axis and change the sign of the rotations on the other axes. That means you have three choices: X, Y or Z. The typical choice is to do it along the Z axis, which LightWave does. Unity uses the X axis, which results in an apparent 180 degree rotation of the scene.
Another oddity on FBX import is the wrong rotation of Lights and Cameras, caused by Unity ignoring any pre-rotation setting stored in the FBX file, so these need to be compensated as well, again only for Unity.
Using this switch means that when you go into Unity and look down the Z axis the imported FBX looks exactly the same as it does inside LightWave.