In Impress, there is a slide overview sidebar on the left. Logically, to create a new slide, a user looks for a button on or near this sidebar. The create new slide button on the toolbar is in the top right in the second row by default however. This is confusion and unintuitive.
In Impress the Slides preview "sorter" pane does have a context menu action of "New slide".
The "create new slide button on the toolbar" referred to is actually an element of the "Presentation" toolbar. Which is by default docked right of the "Standard" toolbar. But can be redocked as preferred, or simply undocked and allowed to float.
As it can be moved should a user prefer, there is no issue with its default docking right of the Standard toolbar. Alternative docking below Standard toolbar would otherwise consume vertical space, and users would object to default docking left of Standard toolbar.
I have suggested the same thing in bug 89668 and you can see the mockup i've made for it ( attachment 113696 [details] ).
*** This bug has been marked as a duplicate of bug 89668 ***