Imagine that you’re editing a 20-minute project, and the timeline window is zoomed into a 30-second portion of it.
The time marker track above the timeline is for detailed clip placement on the currently visible portion of the timeline (a 30-second portion in this case). It isn’t really for scrolling… it’s more for moving the playhead within the current view to enable precise adjustments, and for providing a sense of location within the larger project.
This moves the 30-second zoom window to a different portion of the timeline, since the entire project cannot be seen on the screen at once while zoomed in.
Scrolling with the mouse wheel accomplishes the same thing.
This one does double-duty. The preview window has two tabs under it for Source and Project. If the preview is for Project, then yes, it could be somewhat redundant. But more often, that time track is used for the Source window when setting In and Out points on a new clip before dropping it onto the timeline. It is effectively scrolling a separate video than the timeline.