I may want to add that this happens because the ECB(Environment collision box) updates during hitlag.
If you hit your opponent early enough after dropping through a platform, the ECB looks at your position and finds that you should be on the platform.
I don't think these platform cancels are something anyone except a pro should consider practicing, but in the following post a possible application of platform cancels is shown:
http://smashboards.com/threads/official-ask-anyone-frame-things-thread.313889/page-26#post-20232163
I would say you should only be aware of platform cancels, know with which moves it might happen when you drop through with an aerial ASAP. Doing platform cancels consistently requires too much practice that could be spent on something more important.
I'm not completely sure about this but I think the ECB also updates when using specials or airdodge. (
@Kadano halp pls)
I think so because when you do a special at the exact platforms height in the air, you do that special grounded and on the platform. This way you can shine-grab instantly on a platform out of full jump like shown in the following video:
For falco this only works on battlefield and yoshi's due to the platform height out of a full jump. There is no (full) frame on which you are on the correct height on stadium and dreamland.
On the same height it is also possible to waveland horizontally, which gives you the highest possible waveland speed.
Fun fact: sheik is faster during a horizontal waveland than when running.