[media=youtube]8yB_QiRfMoY"[/media] Some uses with Snake.
http://ca.youtube.com/watch?v=GUX5cf5VQNY Some uses with Yoshi. Check towards the end of the vid for the more useful stuff.
With most characters, the landing lag isn’t so bad that SHing or FJing an attack, landing then repeating isn’t a problem. But, some characters like Bowser/DK/Ganon have more landing lag than others, making this tech somewhat useful for them.
Also, since it allows you to use your second jump from the ground for an aerial approach, it allows another angle of attack. Take the video of Snake above. His second jump is higher than his SH or FJ, so he can use ISJ with his aerials to decrease landing lag and remain in the air.
Falco is another example. His SH is very low, and his FJ is very high. ISJ allows him to gain an approach somewhere in the middle.
Dedede can chase and combo aerially with Uair, then fastfall and ISJR the last Uair and get all of his jumps refreshed, allowing him to hit with an immediate Bair near the ground.
Evidently this can be used with some B attacks too. For Ness SideB, cutting out the landing lag is quite useful, as he lags a lot aftern landing from SideB.
As it is still fairly new, the full uses of it haven’t been found yet. Odds are, it’s something that’s sort of trivial, as landing lag isn’t an issue for most characters. But, being able to use your second jump repeatedly from the ground allows you to chage the height/angle of your approach, something that could be useful, especially with characters like Snake, whose second jump is arguably better than his SH or FJ. I linked it here because I thought some heads here might be able to figure out a use or two for it.