I tried using Windows Explorer to do it. Windows Explorer is what you see when you open "My Computer" and look at the contents. It's what you see when you open "My Documents" and see the contents there. It's a simple window interface to your file system so that you can manage your files.
Comparing folders with Windows Explorer is slow and cumbersome. It takes time to scan the timestamps on files and folders. It takes time for humans to compare the contents and remove what isn't needed. It's not that easy to find duplicates.
So I did some searching around. I had used Directory Opus before when was I still on the Amiga and figured there was something out there for Windows. So I looked around for file browsers and found Beyond Compare by Scooter Software, tested the trial version, bought a license (for work and home) and never looked back. Beyond Compare provides a 2 or 3 pane interface for comparing files by date, size or whatever you like. See the screenshot below:
With this program, I can compare files at a glance between directories. I can sort them by date, size or name. When I want to merge folders, I don't have to worry about overwriting files - Beyond Compare will not overwrite a file that is newer than the source file. In other words, when syncing two directories, it will check each file pair and if the destination file is newer than the source file, the file will not be copied. If the source file is newer than the destination file of the same name, the file is copied to overwrite the older file. If the file does not exist at the destination, the file is copied.
I've used this program to eliminate more than 60 GB of duplicate files in a previous job. This would have been a tedious expedition to perform by hand, easily lasting days to complete. I say expedition because there is no real safety net when copying or merging in Windows Explorer. Beyond Compare made very light and interesting work of sorting through all of those files.
I see that Directory Opus is still out there. But they only make a version for Windows. Beyond Compare runs on Windows, Mac and Linux. If desired, you can get a multiplatform license that allows you to run the program on all three. It's a per seat license so as long as you're using it on one computer at a time, you're in the clear.
Now I use it at work to manage files I collect in the course of my job. I have to store them on my computer at work and then back them up to a network folder. Beyond Compare makes it easy for me to compare the local and network folder, sync them up and delete what I don't need to keep so that my local drive doesn't fill up. When I start work for the day, I start Beyond Compare and let it scan all the folders while I start up everything else. Then at the end of the day, I sync up again and delete what I don't need on my local drive.
Note that Beyond Compare can be scripted to perform a sync via Windows Task Scheduler, too. I have used this function and found it to be very useful. This feature allows you to take any comparison session and run it as a script. Beyond Compare scripting is simple and intuitive. If you find that you need to automate folder syncs, this is the tool to use.
Beyond Compare doesn't just compare folders, it can also be used to compare text files. I used to manage configuration files for a document distribution system in another job. These files were large and can be confusing to navigate. Sometimes, I made an error and that caused the distribution system to fail. Then I would have to put the old configuration file back where it was until I could figure out what went wrong.
Beyond Compare makes it easy to do a line by line comparison of two files so that I can find the changes and check for errors. When comparing files, it highlights the changes in red and also provides an overview of the entire file so you can easily zero in on what changed without having to visually scan each line. With Beyond Compare, I was able to find a single missing semicolon in a file hundreds of lines long by comparing the new file to the old file. That would have been very difficult to do by eye to meet the deadline I was facing.
Now normally, I would not be singing the praises of proprietary software like Beyond Compare. But I have looked long and hard over the years for a better product or program for Windows or Linux and found them wanting. Yes, there are open source solutions, but none of them are Beyond Compare.
If you are faced with the task of consolidating files in your organization, Beyond Compare can do the job and make short work of it. If you are a programmer, you will find that the text comparison functions of Beyond Compare can reduce eye strain when you're looking for changes in your files or searching for that one error that makes you lose sleep at night. For myself, I have peace of mind knowing that I will never overwrite a newer file when I merge folders, thanks to Beyond Compare.