On most forums, websites and so on, when someone asks "do I need to defragment my Linux filesystems?", the answer is "no". But that's a common misconception and in some cases you do have to defragment your Linux filesystems.
I know everybody says EXT3 and EXT4 filesystems don't need defragmentation and in most cases, that's true! But sometimes they actually do need defragmentation. There is an entire discussion rather or not EXT3 needs defragmentation but I'll not get into that. It just depends on the way a filesystem is used, when it was last formated and how full it is.