Usually when Sora tries to attack a box in such a position, it either pushes him out or doesn't work. However, if you manipulate the DS camera on the lower screen to be slightly off from the way it usually is, it lets Sora attack and move the box towards him without pushing him out.

This seems to have no uses in a TAS.

In the final system sector for Traverse Town, you'll come across a formation such as this. If you attack the boxes in the right position, when they fuse they'll push Sora forward instead. This saves about a second over fusing them normally and destroying the box to proceed.

Slide Dashing in a certain spot away from the cutscene trigger allows you to skip it. The trigger itself disappears once you do the events in the alleyway.