See discussion in D4323, this is mostly a question of changing defaults.
It's not entirely clear to me how this applies to the different platforms.
On Mac, the convention is to *not* start apps in full-screen. Full Screen on the Mac is a special mode that makes the dock and menubar disappear. It's useful, but it's not expected that an app starts this way.
So, I think we should follow the platform conventions, if possible. If the convention for pro apps on Windows and Linux is to open maximised, then it makes sense to do it there.
Edit: I tested it here, and it doesn't seem to affect Mac? So in that case, if Linux and Windows users approve, then it's all good.
This will not start Blender fullscreen, only maximized. On macOS there isn't really a maximized state, just windows that are resized to cover the entire screen except the dock and menu bar. For a typical Mac laptop this change will make no difference as the Blender default window size is already big enough to cover the entire screen. For a bigger screen it will start Blender bigger, which I think is still a good default.
Well, on Mac, maximized and full-screen are really the same thing.
Anyway, here it seems that it restores the previous window size on Mac when you launch Blender. So this patch doesn't really affect macOS at all in practice.
Since this mainly affects Linux/Windows, I will defer to people who are more familiar with conventions on those platforms.
like most other programs, Blender should save the location and size of the window when closing and restore when opening
full-screen - green button
maximize - double click on window top-bar (or Window > Zoom)