Detailed information about the 3D structure of a protein can help us to understand the molecular basis for biological function. High- and medium-accuracy comparative models can help refine function prediction. Ligand binding is directly determined by the structure of the binding site. It is also possible to predict features of the target structure that do not occur in the template structure. Modelling can be a way of extending the set of known 3D structures since experimental techniques are relatively slow and expensive.