Hi, the hidden defragging does not cause any undue wear and tear on your hard drive. I have been using iObit SmartDefrag until recently. I always had a full Green rating of excellent - however, on checking the state of fragmentation using XP's own defrag I found that even with the excellent rating in iObit, my drive still showed quite a lot of fragmentation. I have therefore changed to using Diskeeper from click here and have found this one to be rather better. Diskeeper, like iObit, also runs quietly in the background keeping my three hard drives fully defragged.