I am not sure either whether S.Vortex should be in the main board.
It is surely a great side board card, no need to argue there.
To give more examples of its use, on top of the added pressure it naturally brings:
vs DnT, it prevents them from coming back with a Batterskull or Jitte (which is usually the doom of our deck when it lands),
vs Reanimator, they won't take full advantage of their Griselbrand (can draw but not gain life),
vs Deathrite Shaman, well they can still use 2 of its 3 abilities, just not gaining life,
vs Punshing Grove combo, they cannot bring back the P.Fire (thus keeping your criters relatively safer),
vs MUD, blanks their Glimmerpost plan as well as the Wurmcoil one,
vs Loam/Eternal Garden, prevents their Zuran Orb B-plan
vs Leyline of Sanctity, you are golden since the Leyline won't prevent the Vortex from hitting them (OK, this is a fringe situation since your opponent will probably not side these Leylines vs UR delver -unless you managed to hide the U spells from them for the whole G1-)
...

However, just as a reminder, S.Vortex is a shitty idea vs Infect.deck 'cause this won't prevent them from casting their Invigorates for nothing.