If you buy the in-app purchase you are able to selectively download files to the local device.
This setting is called “Download Files” either “Always” or “On Demand”.
When this is set at the database level (Tap and hold the database, select “Info” and toggle either “Always” or “On Demand”), this setting sets a default. Any existing file will follow this setting immediately. Subsequently added files will either be downloaded or not based on the database-level setting.
Individual groups have their own setting that can differ from the default database-level setting.
For a given database:
If you want MOST of the groups to be locally downloaded but have only a few you want excluded, set the database to “always” and then change the setting to “on demand” for those few groups. (Note, Groups added on other devices and synced over WILL automatically download to the device)
If you want ONLY A FEW groups to be locally downloaded, then set the database to “on demand” and selectively change those groups you want to “always”. (Note: Groups added on other devices and synced WILL NOT automatically be downloaded to your device)
The other setting to concern yourself with is the “Schedule” setting in the global app settings at the app’s home screen.
Automatic means that the application will only keep the most recently viewed/modified X files, where X is a number like 500 controlled by the slider. This means that files you haven’t touched in a long time in “on demand” databases or groups will automatically be purged. their metadata is still present, but if you want to view the contents they’ll need to be re-downloaded.
Manual means it’s up to you to selectively purge downloaded files you no longer want stored locally (but, of course, can be downloaded at any time again).
NOTE: “Purge” does not remove the file from the database, it simply removes the contents of the file from the locally stored database. The metadata will persist, it will still show up as a member of the group, it will still show up in search results, but if you want to view its contents you have to re-download it. This DOES NOT affect the file on any other devices. Purging it from your iPhone will not, in any way, impact your Mac, or another iOS device, etc.
Hope this helps!