Two types of mixed models in ANOVA. A mixed model is one with both fixed and random factors. A restricted model requires the crossed, mixed terms to sum to zero over subscripts corresponding to fixed effects. An unrestricted model does not require this. Many textbooks use the restricted model while most statistics programs use the unrestricted model. Minitab fits the unrestricted model by default, but you can choose to fit the restricted form. The reasons to choose one form over the other have not been clearly defined in the statistical literature.
The option to choose between the two only occurs with a mixed model in Balanced ANOVA. Your choice of model does not affect the sums of squares, degrees of freedom, mean squares, or marginal and cell means. It does affect the expected mean squares, error term for the F-tests, and the estimated variance components.