Safety spools and reels both hold line, but usually have different uses. Reels usually have a handle and a winding knob and hold more line than a spool. Spools are much more compact and have no moving parts. Spools are used to deploy SMBs, safety floats, and lift bags. Reels are used to deploy larger amounts of line for exploration. Although spools look simple and less complex than reels, spools actually require more training and practice than reels do.