sree205, are you sure?
from the point of power dissipation, though, the power stripe width of std cells is fixed(when design std cell, the load of the power wire will be considered, so how much of std cells can share the power wire is fixed at most),i think it is not useful as you said, becasue you can use thinner power wire when you use the power stripes only for one row of standard cells.
i think the main reason is reducing area, because the space between two power stripes is necessory.
in addition, i think how you place the standard cells depends on the library.for example,if the library is not designed to back-to-back placement, you cannot do that.