This functionality is in beta and is subject to change. The design and code is considered to be less mature than official GA features. Elastic will take a best effort approach to fix any issues, but beta features are not subject to the support SLA of official GA features.
Keeping historical data around for analysis is extremely useful but often avoided due to the financial cost of archiving massive amounts of data. Retention periods are thus driven by financial realities rather than by the usefulness of extensive historical data.
The Rollup feature in X-Pack provides a means to summarize and store historical data so that it can still be used for analysis, but at a fraction of the storage cost of raw data.