Models of technical parts of farm systems have proliferated over the past decade. In this paper, the difference between the decision-information deriving from the farm management economic analysis that is included in a technical systems model, and the results derived from analysing the technical information that comes out of the model using standard farm management tools, is demonstrated, using case studies. In essence the argument of this paper is that in much systems simulation work provides sound technical coefficients about the operation of a farming system, which can then form the basis of, and be used in, whole farm management analyses. It is sufficient, to provide these coefficients without the systems model itself linking to some half-baked ‘economic’ analysis. In technical systems models destined to be decision support tools it may well be the case of no economics is better than some!