Use case or problem
When on mobile some people may have a mobile data contract with limited metered data. As background sync is not a thing yet on mobile, new (big) attachments (like PDFs) are not automatically synced when connected to WiFi at home. So when leaving the wifi network and opening the mobile app all these attachments are being synced then, on the metered connection, using up a significant portion of the metered data.
PS. This may be a unique request as I am living in a country where limitless data contracts are still very expensive.
Proposed solution
In the Sync core plugin an option saying “Sync only markdown files on metered connection” would prevent the download of all attachment files that are not “.md”, while still keeping the vault up to date for the markdown notes.
Current workaround (optional)
When opening the Obsidian Mobile app on metered connection, directly pausing sync and disabling the syncing of all other file attachments in the Core Sync plugin, then resuming the sync. When connecting to WiFi again, the sync options for attachments can be enabled again until disconnecting the WiFi again.