The point is not to scare out Jellicent but to be able to threaten her with a ko in order to be able to spin. And Sandslash in sand can scare out quite a few pokes, such as Heatran, Thunurus-T, Tyranitar, Terrakion and more.
For example +2 Earth Plate Adamant Sandslash does 82.87 - 97.76% with EQ to 252 / 216+ Jellicent, so after SR and sandstorm damage, Jellicent has a 68.75% to get ohkoed if it was at full health.
And use Earth Plate on Sandslash guys it is good, especially on Rapid Spin Sandslash. You gain the power to ohko all OU spin-blockers, while not jeopardizing your bulk. If you run SD + 3 attacks though, you are better off with LO, as Sandslash needs all the power he can get to sweep.
My calcs were wrong, so ok, you have your point there.
However, Scarf pokemon that reach 459 can outpace it. What's more, if you mistake the pokemon you're "scaring out" for any other set then Scarf and try to SD on, for example Terrakion, you'll be the one forced out. Sure, it's not something that will happen over 80% of the time, but just food for thought that set up fodder is not always set up fodder. And another testament to how slow Sandslash is. Scarf Lucario and faster can outpace (disclaimer: this isn't saying that Scarf Lucario is common, just to show what can outpace).
It can't rip most offense teams apart, as Air Balloon pokemon can check it. And no, please don't use the "it may flinch" argument, as I'll use the "it can miss" argument and we'll all be sour. Air Balloon Lucario is immune to flinching and can KO with Close Combat followed by Extremespeed (87% minimum). Or could wait till you're around 53% and counter sweep you instead (SD, then Espeed, then gg). Or you could run scarf pokemon.
Why am I showing all of this? Because even if you do KO the spinblocker, the scarfer or Air Balloon pokemon will happily KO you or do a chunk against the switch in. But wait, why does a offensive Sand team need a spinner that badly? There are usually no SR weak pokemon, it's OFFENSIVE, which means give the opponent as liittle oppenings as possible, so...uh...yeah, I don't know why you should use Sandslash as a spinner, as Starmie can KO the spinblockers as well, while Starmie can at least somewhat handle Forretress, beat Skarm easy...which Sandslash can't. And unlike Starmie, you can only use scarfers in all weathers to check it, not like Sandslash who needs Sand in order to outpace anything (while still being outpaced). Not to mention you'll put even more pressure on the water resist, unless you like sacking something every time that Politoed comes in.
But that's just me, as I prefer weatherless offense. Maybe I can get a explanation as to why Sandslash should be a spinner?