Not everybody uses 2.5" HDDs for a laptop. Like the guy in previous post before mine who has two of these drives in his Mac Mini. ^^
You are correct in saying that laptop users should not want to disable or increase the head parking timeout. But for other users this can be highly desirable feature.
On a desktop machine with no battery then there is going to be few benefit to be saving the 2 watts going to sleep all the time. Not that the power saving will even be so much as that if the drive is continuously being woken up again.
For example, did you know that on FreeBSD+ZFS, the short timeout actually interferes with ZFS's read-ahead memory cacheing mechanism, (which reads just slightly less often, e.g. every 10-15 seconds). Thereby causing a continuous cycle of idle --> park --> request next chunk --> wake up --> unpark --> read --> idle --> park.
The problem is not just restricted to freebsd + zfs or server type loads. You would be surprised how easily this situation can happen on a desktop machine. Many other kinds of background software can request access to the disk very often and will thereby also cause this same effect.
Now. These sorts of drives are typically rated for 600,000 load_cycle_count. But you would be surprised how quickly that number can be reached. In fact on my OS X machine i've been using a 750GB Seagate 7200.4 in my Mac Mini for power_on_hours = 12126 /24 = 505 days. In that time smartctl is reporting the load_cycle_count to be 189,9918 already. And that's when it's never even been my primary drive, just using it for a secondary mass storage device and a few big things like my iTunes Library.
----------
I put two 2tb samsung M9t into my mac mini,
Hi tallpaul. If you are still here can you please run smartctl ,etc and post output as described above? Many thanks.