The sidebar merely shows you the hierarchy of groups in your database and lets you navigate them. If by panel you mean the inspector on the right side of the window, that gives you access to all kinds of different things for your files. IMO, if you tried to include all the functionality of these two areas into one, you’d end up with an absolute mess that’s impossible to work with. (If I am understanding your question.)
Learn the keyboard shortcuts to expand and collapse these areas, as well as the ones to jump from one to the other. I am constantly expanding/collapsing them based on my needs, and it is trivial to do so. Hope that helps.