Question about how MD5 checksum option works in FolderSync

[Mr X]

I have some questions about how the "MD5 checksum" option in FolderSync works, which I could not find the answers for either in the help file or in the FAQ.

My first question is how the MD5 checksum is used during the file sync, without downloading all the data from the remote folder during every sync? Because without downloading all the data from the remote folder, how could you possibly calculate an MD5 checksum of the files to use for such a checksum comparison?

Also, if I only want to use date/size checks for the file comparisons during my syncs (in order to minimize battery usage, data transfer volume and processing time during the syncs, and since the contents of my synced files should never change anyway), would this be the effect of simply unchecking the "MD5 checksum" option, or do I need to do something else?

[KaiUno]

Could it be that they're only using MD5 to verify the file after a copy?