Clicking on the green button at the top left of a window used to maximise the window, until it meant making the window full-screen. Since then, double-clicking the window’s title bar (when set in the Dock pane), or Opt-clicking the green button, has maximised the window. These are documented for El Capitan here, and for Sierra here.
This doesn’t work consistently, though, for some Finder windows, particularly those in List view.
When the contents list is much greater than can be fitted into the unmaximised window, it works fine. Maximising the window, or using the Finder’s Zoom command in the Window menu, expands the window vertically (and horizontally, where necessary) to fill the Desktop. In the screenshot above, the window on the left is unmaximised, that on the right is maximised.
Repeat the same with a contents list which is only a little greater than the current (unmaximised) window, and the maximised window is still insufficient to contain the complete contents, and falls far short of filling the Desktop.
In some circumstances, Sierra 10.12 and 10.12.1 seems to show other bugs in maximising List views: these are detailed in the comments to the list of bugs in macOS 10.12.1.
None of these is catastrophic, and we can work around them, but they are messy, inconsistent, and indicate fairly simple shortcomings in the Finder.
I have added them to the list of known bugs in macOS 10.12.1, although some of them seem to be rather older.
(Thanks to Gaz for reporting these, even if I can’t replicate them all here.)