So, you should close your sidebar. You know why? It saves you screen space! You can gain up to 120 pixels by closing the bar. But you say that if you close it, you won’t be able to see the sub-items without reopening? Not so!
I don’t believe this feature was available in 2.7 but as of 2.8, you can hover over the closed menu parent item and a submenu will appear next to it. You can try it easily by just closing your sidebar and hovering over the little pin icon which represents the Post menu.
This is by no means revolutionary but it is something to keep in mind.