If you are saving changes to a list, and that list is referenced by 6 or more other lists, you'll see the following warning:
When a list that is used as a filter in other lists is edited, that prompts changes in the dependent lists. For most lists, the reprocessing of these other lists won't take very long -- maybe a few minutes. However, if your dependent lists use more complex filters, such as email clicks or page views vs just property filters, it may take even longer to process.
This is important because you won't be able to complete actions like emails or exports on those dependent lists until they finish processing.