If you are like me and have multiple backups of certain folders that you need to keep up-to-date on multiple harddrives this tool will be very useful.
It is built into MacOS and called FileMerge.
Then find one of the folders and put it on the left and the other on the right, then click compare.
FileMerge will take some time to compare everything but eventually it will contain a very easy to understand comparison of the 2 folders.
Very simple tip but I find this invaluable when updating backup folders and of course keeping source code up-to-date.