The talent Voodoo Totem for shamans is an instant-cast totem which hex all targets in an area. This talent replaces hex, and once you talent into voodoo totem, hex will be removed from your spell book and can no longer be cast.
However if you have learned one of the cosmetic glyphs for hex such as Compy Hex, Spider Hex, Snake Hex, or Cockroach Hex, these these will not be removed from your spell book, and you can still use these in addition to Voodoo Totem.
This is clearly unintended as voodoo totem prevents you from using the generic frog hex. The usefulness is probably limited to high end mythic+ content and maybe PvP though.