There may come a time when you will need to move data from one source to another.  You could always use Windows Explorer to do this, but you will not be able to retain any metadata in your library.

Recently, I needed to move around 1,200 files (680 MB) from a folder into a new document library.  I tried using Windows Explorer but as I stated earlier, it would not copy over the metadata.  Then, I tried using Content and Structure.  This has worked for me in the past and it will preserve your metadata.  However, this time around, I was unable to copy the files.  Not sure why, could have been file size or just the environment.

After all of this, I ended up opening my site inside of SharePoint Designer.  Within 2 minutes, I copied all of the files and preserved all of the metadata associated with the files.

To quote an old southern saying, there is always more that one way to skin a cat.  Just got to find the right one.