As a standard scroll-wheel mouse user, horizontal scrolling on the web is a pain. You’re stuck either clicking and dragging the scrollbar, or you’re forced to use both hands to use a shift modifier. Dragging the scrollbar takes some precision, so it can slow you down. Using 2 hands is its own issue, but the scroll speed isn’t even ideal when shift is used.
Apps like Trello and Asana solve this by allowing areas like this to be clicked and dragged.