Hard drives get laid out in fairly complex ways. Second-guessing how your disk heads move as part of a decision whether to use multiple partitions is not really a practical way to save a hard drive from failure.
Fragmentation is about how a file is stored on a disk and is not preserved across a copy. In fact, in some cases you can defragment a hard drive using copy.
Defragging rearranges the layout of files on your hard disk for faster access. Specifically when (or even if) you need to do it at all is evolving.