Is there any advantage to lower efficiency speakers? 87 or below?

Ok extended bass.  I knew these dali ms4's were suppose to sound best away from the wall and now I know why.  My only concern would be if I wanted to pair with a lower wattage tube amp in the future. With that said, Johnny Cash sounds unbelievable on these speakers.  The extension shows up in a big natural way.  

Thanks everyone!  These are really good explanations.