It’s very common that I want to hide the side bar to free viewing space on the left. The current behavior widens Sublime’s view into the space left by the hidden sidebar. I think an option to hide the side bar be simply hiding it in the rightward direction rather than expanding the window would be useful.
Hide side bar by reducing toward the right
Are you asking about resizing the window smaller when the sidebar gets hidden?
Yes although maybe it would be awkward if the window shifted away from the mouse when using the GUI button