One of the major selling points of MongoDB is scalability. It has been designed with features that are supposed to help your application scale out. If you are developing your application to be highly scalable, and your use cases fit into one of those advantages of GridFS we discussed earlier in this chapter, you may consider it as your asset storage backend. But for a website that experiences small to medium traffic, serving files over GridFS rather than the filesystem is an overkill. As Martin Fowler rightly says, "Premature optimization is the root of all evil."
Also, benchmarks show that for serving small static files (JavaScript, CSS, and so on, on your website), using Apache or Nginx web server over the filesystem is faster than GridFS (Chris Heald has a very informative post on his blog available at http://www.coffeepowered.net/2010/02/17/serving-files-out-of-gridfs/). So you should stick to the filesystem if you only need to serve small files over HTTP...