code: def _save_fastq_space(items):
      
      to_cleanup = {}
      for data in (utils.to_single_data(x) for x in items):
          for fname in data.get("files", []):
              if os.path.realpath(fname).startswith(dd.get_work_dir(data)):
                  to_cleanup[fname] = data["config"]
      for fname, config in to_cleanup.items():
          utils.save_diskspace(fname, "Cleanup prep files after alignment finished", config)
docs: Potentially save fastq space prior to merging, since alignments done.