Does the maintenance plan delete data? If so, How can I know what data is been deleted?
The maintenance job doesn’t delete any data and only rebuilds indexes.
The Spotlight Statistic Repository database deletes data based on the retention time set from "Configure | Scheduling" - look at the "Keep for" column.
The Spotlight Playback database deletes data based on schedule set in "Configure | Diagnostic Server | Playback Database." Look under "Store Playback data for."