I would use /E if I only wanted to copy the directory structure not /MIR. /MIR also does a purge. So if you have files that exist on the "repository" server that no longer exist on the source server it will delete them. Since the original request said he wanted to move the files /MIR would not work as the second time you ran it it would purge all of the files you moved in your first batch.

I do however use the /MIR option. For instance I have three servers that contain my staging data for new servers. Because I deploy servers all over the US I have different staging points at different geographical/network locations to speed up copying large install files. What I do is update only the primary staging share and then use robocopy with the /MIR option to automatically copy new files, and delete old files that are no longer needed.

It really is powerful when you start to look at all the possible combinations of switches you can use.