Some might answer that in the case of coil failure, it’s cheaper for the owner to replace the coil that has failed rather than replacing two coils. That might seem acceptable for the owner initially, but it will cost more in the long run; the system will not run as efficiently as one in which the coils match. That’s especially true if the remaining coil is more than five years old.
Another problem is that mismatched coils can put additional stress on the cooling system, which may lead to premature failure. Then the owner could be looking at replacing the whole system, which probably isn’t going to make him happy. Installing matched condenser and evaporator coils makes sense, because customers will receive a reliable, efficient system that provides the highest level of comfort.