Why don't I have a custom title by now?!
I don't know about fragmentation, but I recall reading that it supposedly made data recovery easier, since every cluster actually contained a pointer to the next cluster for a particular file, therefore bypassing the problem you have with the "first free block" allocation strategy used on FAT or NTFS.
I would like to think that the HFS file system is better. However I have never had a problem with NTFS ether. I was told in school HFS handles fragmentation better.
There, if you delete a file and immediately write something to disk (even if you don't overwrite the actual file data), just recovering the FAT/NTFS entries is not enough: if the cluster chain information is destroyed, and the file was not in one piece on the disk, locating just its starting cluster will do you no good, while on HFS you can hop through incredible levels of fragmentation, assuming the clusters themselves weren't overwritten.
In any case, the fragmentation problem inherent in FAT/NTFS seems to be more due to the simplistic allocation strategy used ("find next free cluster on the disk in an incremental fashion, even if it's ONE cluster sandwiched between two used ones"). The advantage is that you waste almost no time finding a suitable free space for a file. The downside is, well, easier fragmentation.
Most Linux filesystems actually use a more time-consuming strategy for locataing a suitable space ("find enough contiguous clusters for holding the entire file, plus some leeway"). So you need more time to find free space, but the tradeoff is supposedly worth it. NTFS is supposedly a bit smarter than FAT, e.g. it DOES search for large free space for large files, but nowhere near as good the linux/ext strategy.
I guess it depends on the software you use, and its read/write patterns. E.g. Audacity stores many small files (more prone to fragmentation), other programs may save larger continuous streams etc.
I was also told you should de-fragment your audio drive not your OS drive. I have found the opposite to be true. I can Explain if anyone is interested.
The OS disk is ALWAYS under pressure (millions of R/W I/O on small files everyday), so of course it needs more defragging...unless it's ext3/4, of course.