If you write a file to disk, then wait fifteen minutes before deleting it, chances are the OS will have flushed it to disk sometime in the meantime. It won't have to re-read it if there's still free memory, but it's extra load on disk io.

If you write a lot of them, then even if you have the memory, you may overrun the size limit of the write buffer and cause application stalls.

Writing to a ramdisk (e.g. tmpfs) is always an option, though.