If you buy a ferrari, do you drive below the speedlimit to save gas? 
Running a 1080 on 100 watt is possible, but the speed in only 31MHASH. If you run@ 150 watt you get 36MHASH (sp-mod #3)
Running a 1080 on 100 watt is possible, but the speed in only 31MHASH. If you run@ 150 watt you get 36MHASH (sp-mod #3)
using the same electricity, you can run 3x1080 @100W each, total 93 Mh/s; vs. total 72 Mh/s @150W each.