Short answer: It's not needed.
Longer answer: Linux is smart enough to first attempt to guess the size of a newly created file, and hence reserve that much space for it, and then when reading re-order the requests
instead of having to move the files physically. That's one of the advantages of being built on a multi-user base.
For en even longer answer, see this post
Now, a couple of new and fancy file-systems add a background defragmenter (that might also do other things), but for the most common filesystems it's simply not needed, at least in the sense that the system loses a lot of performance if it's not regularly defragged.