When doing a sync rclone will find the intersection of the source and destination hashes. If there is more than one in the intersection then it will pick one of them to use. It actually picks them in the order shown here
$ rclone hashsum
Supported hashes are:
* md5
* sha1
* whirlpool
* crc32
* sha256
* dropbox
* hidrive
* mailru
* quickxor
So this could be useful if you wanted to sync from sftp to local but use SHA1 instead of MD5 for some reason.
Can you think of any other use cases? Maybe this makes it a sync/copy/move flag?