When editing a page in the panel there is a sidebar. It can be good for going to subpages and so on but sometimes it can be good to use the whole screen for the fields.
As far as I can see I can’t close it or hide it. Some toggle-switch would be great. It would also be great to set the default state of that sidebar, hidden or opened.
I don’t know if I necessarily agree with the qualm, but for your editing pleasure, you might add a bookmarklet that toggles the sidebar on and off:
In Chrome, you can click on the bookmarks bar and select Add Page, then paste this into the URL field.
Edit: I take no responsibility for any damage or confusion this causes.