It is also used for getting the super heat at the evaporator. Being able to get an accurate superheat for THAT ( mainly non matched systems ) evaporator will tell you if you are starving or flooding it which either way is wasting efficiency. It is also useful in determining suction line restrictions having two pressure references at either end of the suction line. Getting the superheat at the evap coil will give you a more accurate read on how your refrigerant is boiling off or not within that coil where as taking it at the condenser wouldn't necessarily show if it was flooding a bit and boiling off within the suction line, especially so for long line sets.
"I am for doing good to the poor, but I differ in opinion of the means. I think the best way of doing good to the poor, is not making them easy in poverty, but leading or driving them out of it."
Benjamin Franklin, 1766