If you are looking to compare two folders or files which have almost similar content, then check out WinMerge a tool which can help you with many things for free, since this is a Open Source Tool for Windows.
If you have a project which is being updated and you want to compare the changes made in a number of files or folders, then doing it manually can be a tedious job and a tool like this can come handy because it takes minimal space for installation and it handles multiple file formats ie Windows, Mac & Unix.
If you see the above screenshots you can file how easy it would be to compare two text files with line numbers, word-wrap and highlighting of the changes in both files. The Folders are compared based on the file sizes and dates and you can compare big folders with all sub folders.
Just download the application and install it to get started with your comparisons.