Simulation software and model reuse: a polemic

Is it really true that simulation models and simulation software should always be regarded as candidates for reuse, or is it better to be selective? What are the obstacles to simulation software and model reuse? Can these be surmounted and, if so, at what cost? There is a range of levels at which simulation software may be reused, a range of costs to be borne and range of benefits that may be achieved. It is crucial to consider the issue of validity when considering model reuse and this needs to be a fundamental part of any reuse strategy. There may be circumstances in which reuse is economic, especially when a small, low-fidelity model will suffice.