Are you talking about background maintenance tasks run automatically sometime between 3:15 AM and 5:30 AM (your local time). The disk activity generated by find is a normal part of file system maintenance, used for tasks such as removing invisible temporary files that are used by the system. In Snow Leopard (v.10.6), those tasks do not run when the computer is asleep, and will run after it wakes from sleep mode. (Knowledge Base HT2319
The fragmented disk would not affect the disk much thanks to the file system used in Mac OS X. There are some disk defragment utilities available, and if you want a piece of mind, you are free to use those.
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