There are many usecases for symbolic links but one time they are a must is when developing your own composer packages.
When developing packages; you will want to be able to test the code in another project. First problem you might encounter is git repo inside another gitrepo = submodules. So easiest after cleaning up that mess is to move your package outside of testing package.
Now you want to be able to run composer update and install it like normal, but you also dont want to run composer update every time you did a change. You also do not want to edit inside the vendor folder since that would mean you copy files manually back to the original folder.
The solution to all of the above is symbolic links, which come in two variant on windows, NTFS junction points or symbolic links. NTFS junction points can only be used on directories, symbolic links can be created to all files but only by administrators.
Here is an example: