Strangely enough rclone sync ~/emptydir targetdir [1] happens to be my favourite way of cleaning up directories used as ad-hoc workplace for all kind of messy stuff: It's perceptibly faster than rsync -r --delete ~/emptydir/ targetdir (not to mention rm -rf targetdir/*, which is still slower and bails out in case too many files are in the top level)
[1] always keep this empty directory sitting in my ~. For some time in the past I even had defined an alias rre='rclone sync ~/emptydir'