To paraphrase a famous soliloquy:
To defragment or not to defragment: that is the question:
Whether 'tis nobler in the mind to suffer
The slings and arrows of outrageous fortune,
Or to take arms against a sea of troubles,
And by opposing end them? To die: to sleep;
No more; and by a sleep to say we end
The heart-ache and the thousand natural shocks
That flesh is heir to, 'tis a consummation
Devoutly to be wish'd. To die, to sleep;
To sleep: perchance to dream: ay, there's the rub;
For in that sleep of death what dreams may come
When we have shuffled off this mortal coil,
Must give us pause: there's the respect
That makes calamity of so long life;
For who would bear the whips and scorns of time,
http://www.artofeuro...speare/sha8.htm
Any use of the hard drive uses up the time that it has to live and that is documented in its Mean Time To Failure (MTTF) and Mean Time Between Failures (MTBF) statistics that are usually measured in years:
http://www.i-mtbf.com
Defagging is a personal choice thing and is akin to personal cleanliness and that too much is paranoia and too little is un-healthy.
So what I do is I defrag before a Windows Update ( makes mental note this is Update Tuesday ) then install the updates then do a defrag and I do a defrag after I have un-installed some applications plus on my Birthday after I have taken the system unit outside and given the insides a good cleaning to remove the accumulated DustBunnies.