I'm curious why when A/C units are installed, why only the cold
Line is insulated from the condenser unit to the evaporator.
Why is the cold line not insulated on the inside of the condenser
Unit?. seems like an energy waste. Questions:
Is it OK to insulate the cold line inside the condenser unit ?
If not, why ? If so, would I see better efficiency?. thanks

The reason the cold line is insulated is so that it will not have condensation on it and possibly drip on ceilings or other things that would be damaged.
The cold line in the condensing unit is the gas that has been through the evaporator coil and has done its job of cooling and is going back to the unit outside to be condensed and preasurised. Ad if the line did have some condensate on it it would not create any problem.