Another reason for choosing sidebar like functionality is that the number of tabs is effectively unlimited. I never understand why developers chose to use tabs for grouping lists of things that can grow unbounded. Eventually you get to a point where you are forced to:
- shrink the tabs ever smaller
- implement scrolling of tabs(!)
- limit creation of new tabs
- auto close them
Sidebars have none of these problems. Tabs should only be used when the number of items you have is known, limited, and ideally a small number.
True but you can easily have 30-40 items in a list, all readable without having to scroll. Text labels are a small fixed height, but a long and widely variable width, so it makes sense to stack them rather than put them end-to-end.
Also a scrolling pane is a standard UI element that is well accepted by users.
