Re-opening because of a request to reconsider this functionality for LabVIEW now that LabVIEW NXG has been discontinued.
By default, the mouse scroll wheel scrolls the block diagram or front panel vertically, CTRL+SCROLL scrolls through cases/events/sequences and adding the SHIFT modifer to either accelerates the scroll. In order to scroll horizontally, however, the mouse has to be hovering over the horizontal scrollbar. Because of the predominant left-to-right, top-to-bottom style of diagram organization, it would be excellent to have a more accessible way to scroll horizontally.
I haven't found anywhere ALT+SCROLL is used - I think horizontal scrolling is a good candidate to fill that spot.