In reading the documentation on Roll-Up Summary Field, I found":
Avoid referencing a roll-up summary field from a child record. The roll-up summary fields referenced from child records can have outdated values, because their parent records have not been updated. Instead, reference roll-up summary fields from parent records. Your roll-up summary fields will always have updated values, because that rule runs after the parent value has been updated.
What does this mean? I created a formula field on child record that references the rollup summary field on parent. Whenever the value of roll up changes in parent it does gets reflected in child record. I am trying to understand what the document statement is about.