Some people like them because it makes it easy to find aliases in a long list of files. The arrow is actually a small “badge” that floats above the file’s native icon.
When you create an alias in OS X (File -> New Alias or Command-L), the alias’ icon displays with a small black arrow in the lower left hand corner. You can use an alias to, for instance, collect all files for a given client (Client XYZ) in one folder, even if your typical filing system is by project and not by client-just make an alias to each of the client’s files (using File -> New Alias or via Command-L), then drag each alias into a new “Client XYZ” folder. As you may know, aliases are small files that point to other files.
