I'm not sure how savvy you are so feel free to skip or ignore stuff! I won't mind. I just like to play it safe and assume people I'm trying to help have little experience :)
If you defrag your drive regularly you are quite likely to burn out certain sectors of your disk more rapidly then the others. This is normal. Each portion of the disc can only support so many read and write routines. When you defrag you rearrange your file system for speed and storage. Thus, you force additional write cycles in particular areas.
In this case, you should- key word being "SHOULD"- be fine. The S.M.A.R.T. would tell you if you were platters were spinning too slowly or were otherwise showing signs of failure.
I hope this helps!
HOWEVER, I always recommend you have backups. I've learned the hard way having lost everything twice. I've burned three drives in the last two years. All of them have crashed and burned without warning. (Two with smoke!) The first reason is because I rescue old drives from my old computers and put them in the new one. The second is that I push my drives hard. I always have some sort of video or music playing and that spins the platters.
(Completely unrelated, one of those drives was burned out by my power supply. It was a cheap thing from M.D.G. which provides minimal quality components. It shorted and introduced a current into the metal case. This, of course, fried my motherboard, central processor, memory modules, one hard disk and a video card. That hurt.)