Gaining process and product understanding is a key element in Pharmaceutical Drug Development. An efficient way to obtain this knowledge is through application of definitive screening designs and other classical statistical experimental designs (DoE). Here, even in application of DoE, “fit for purpose” designs should be selected considering project timelines, resources, effect sparsity, prior knowledge and project goals. The result of these considerations may produce quite different designs from one project to the next. This talk will provide examples of these tradeoffs using illustrative case studies.