I'm experimenting with generating some custom kernels using
However, each iteration leaves a file in
Is it safe to rename and/or delete the
The System.map file is mainly used to debug kernel crashes. It's not actually necessary, but it's best to keep it around if you're going to use that kernel. If you've decided you don't need that kernel, then it's safe to delete the corresponding map file.
If you're really low on disk space, you could compress the map files. They aren't that big, so this won't save much space, but bzip2 will squeeze them down to about 25% of the original size. Then you can uncompress one if you discover that you need it.