To keep diagrams clear and comprehensive, it is best to avoid having too many Expanded Pools in a diagram. Usually, a diagram does only contain one Expanded Pool since every Pool represents their own process in BPMN.
Pools that do not play an important role for the actual process should be collapsed. For example, if the Pool ‘my business’ is important, the processes of the client do not play a role for the actual process. These should be modeled as a Collapsed Pool instead.