This is something I wish I knew years ago.

From Online Tech Tips:

“Ever had to copy a bunch of files from one location on your local hard drive to another place with a lot of files with the same name? Well there are really only two options that you have when there are files with the same name: either replace the destination files or leave the destination files as they are and only copy the new files. 

… 

Luckily, there is still a stealthy way to tell Windows not to overwrite all the files with name conflicts and thereby skip them over. You can create this “No to All” functionality by simply pressing and holding the SHIFT key when you click the No button in the Confirm File Replace dialog box.” 

I like that a lot, Hank

via Lifehacker