My hunch is that's marketing with the service advisors...

I knew a mb alignment tech and they never strapped them down. The did use a spreader bar which is the key. Since most cars are driven msot of the time with only a driver... weighting the drivers seat makes sense- body or ballast. Not sure how they are going to "strap" to simulate that weight distribution- think about it.
Read the W124 manual... nothing about strapping one down there either=0)