new to jj os

i am just starting to use jj, and i keep hearing about simult pad, i dont get why its so important, what is the difference between simult pad and layering the pad in program mode (you get three layers).

JJ took simult out of XL when it was first released. But Its in all the other JJ OS's.
He recently updated XL and put it back in.

video by brother NYM
http://www.youtube.com/watch?v=qa-F9ZQ5TQo