Recently a dispute of the type of Big-Endians vs Little-Endians took place in the Forbes magazine. One reader, Guido Giebens, asserted that the ideal product is one to which nothing can be added. Whereas another reader, Alok Asthana, argued that the ideal product is one from which nothing can be subtracted.
I decided to interfere into this scientific dispute and notice that, in my humble opinion, the ideal product is one to/from which nothing can be neither added nor subtracted without making it worse. (The specification "without making it worse" is important as, generally speaking, something can always be added OR subtracted to/from anything.)
It is easily seen that IFR is a particular case of this definition. Indeed, IFR says that the ideal product/system is no product/system but its function is fulfilled. Thus if we add something to "no product" or to "no system" it will cease to be "no product/system" and, hence, will cease to be IFR. Similarly, there is nothing to subtract from "no product/system". Thus, IFR is ideed a product/system to which nothing can be added without worsening it and from which nothing can be subtracted.
It is also easily seen that a definition of the ideal system as one, which quality parameter(s) attain(s) local maxima is more general than IFR.