I worked for a company that built custom trailers some years ago and learned a few good things such as: When mounting axles we had the trailer frame upside down. After setting an axle in place, whether it was going to be single axle or multiple axles, we measured from the end of the spindle (no tires on spindle yet) to the center point of the hitch on each side. This was an important measurement to make sure the axle tracked straight going down the road. An axle mounted and not being centered correctly would give what we called a "bird dog" track, in other words the rear end would over to one side or the other. So, IF that is what "Denmoor75" is referring to then it is an important measurement.
2015 FR Freedom Express 310BHDS pushing a 2014 GMC Sierra CC