Pareto charts are typically used to prioritize competing or conflicting "problems," so that resources are allocated to the most significant areas. In general, though, they can be used to determine which of several classifications have the most "count" or cost associated with them. For instance, the number of people using the various ATM vs. each of the indoor teller locations, or the profit generated from each of twenty product lines. The important limitations are that the data must be in terms of either counts or costs. The data cannot be in terms that cannot be added, such as percent yields or error rates.
Only Attributes data can be applied to a Pareto Chart.
Learn more about Pareto charts here: