Clarification about -i option of Rclone

Hello everyone,
I need a clarification about the -i option of Rclone. In particular, what does "Important: Since this can cause data loss, test first with the --dry-run or the --interactive /-i flag." mean?

What can cause data loss? The -i option tells if the downloaded files have the same size of the source files?

Thank you very much for your time,
Gennaro Arguzzi

hello and welcome to the forum,

rclone sync can permanently delete files in the dest. so we warns uses about that

it is common here at the forum for new rcloners to make such mistakes.
for example, yesterday, a new rcloner forgot to test with dry-run
https://forum.rclone.org/t/remove-multiple-files-at-once/23356