One big advantage is that once stored, MongoDB offers the same advantages to large files as it does to any other type of data: replication to ensure high availability, sharding to facilitate scalability, and the ability to access a file regardless of the host operating system. Accordingly, if the server's operating system places a limit on the number of files in a single directory, you can use GridFS to store the files and get around OS limitations.
Another big advantage is that due to the way GridFS breaks files into 255 KB chunks, reading extremely large files is not as memory intensive as when you try to directly access the same file stored on the server's filesystem. Finally, using GridFS is a great way to keep files synchronized across servers.
It is recommended that you do not use GridFS if all the files you need to store are less than 16 MB in size. If this is the case, and you still want to take advantage of using MongoDB, simply store the file directly...