TL;DR: Aggregate subitem data up to the parent automatically — roll dates into a parent timeline or sum / average / min / max numbers from subitems into a parent column.
When to use these automations
Project status reports that need an accurate "active project window" on the parent
Dashboards where parent items must show totals or averages from their subitems
Cross-project comparisons where parent-level metrics drive the view
Recipes
Recipe (exact text from automation center)
Use when
Deep-dive
"When subitems date/timeline changes, roll it up to its parent item timeline column."
Parent timeline reflects the actual project window across all subitems.