When is this a problem?
This is a problem when large lists include subsets.
Why is this a problem?
Large lists that include subsets can cause performance problems. They add aggregations and add to the overall size of the model.
How to correct:
Instead of a subset, create a separate list.
More information:
Planual 1.06-02
Questions on this topic? See Are there subsets on larger lists? in our Model Optimization Checklist forum.