Let's say you have created a solid model representing hydraulic conductivity and have converted that model to a Boolean model in which permeable nodes are assigned a value of 1 (for "true") and impermeable nodes are set to 0 (for "false").
Now you want to create a solid model of contaminants from monitoring well data. You can constrain the contaminant model to those areas in which the corresponding node in the Boolean model has a value of 1, to limit the contaminant to permeable nodes only.
Note that constraining models can also significantly descrease the time required to generate the model if the majority of the model would otherwise be subsequently filtered (e.g. multiplying the output by a boolean model).
