Mirror Vs Update in Newer Versions of Toucan

I'm a bit confused about the differences between Mirror & Copy Sync functions. in the help file Mirror is defined as:

"Mirror creates an exact copy of the source directory in the destination directory, it may delete files in the destination directory."

and Update as:

"This copies all of the files in the source directory that are newer than those in the destination directory, it uses the modified time of the files."

If I have a mirror copy of a directory setup somewhere and want to periodically update that copy what would be the best function to run? I have been using update. The descriptions for Mirror mentioned above would suggest that the "Update" option would not delete files in the destination directory if they were deleted from the source?

What function is best in this case?