Datas are available offline, while file synchronization is optional.
Datas
Sheet data are synced periodically. This period is limited by Google quotas and may also depend on the number of concurrent users.
The sync icon indicates when the next sync is scheduled and whether local updates are pending.
Change detection is based on the sheet version history. A new version is generated by Google Sheets after a short period of inactivity after the last change (approximately one minute).
Files
Change detection is also based on file version history. To make files accessible offline, edit the synchronization element of the column configuration.