Both, if possible. Clean before to reduce migration volume; clean after to address any duplicates or residual issues.
Cleaning calendars before a migration reduces the amount of data the migration tool needs to transfer. This makes the migration faster, reduces the risk of conflicts and errors, and means you start the new environment with only the data you actually need.
For shared and resource calendars with years of historical data, a pre-migration clean-up that removes everything older than 12–24 months can dramatically reduce migration complexity.
Run pre-migration clean-up 2–4 weeks before the migration date, so any issues can be identified and resolved before the migration window.
Even with thorough pre-migration preparation, the migration process itself can create issues — duplicate events from overlap periods, historical entries that migrated despite the pre-migration clean-up, or events associated with accounts that no longer exist in the new domain.
Post-migration clean-up addresses these. Sign into WipeAway using credentials in the new domain and clean the affected calendars.
See our full guide: Google Calendar clean-up after a Workspace migration