There should be a option to say if we want real fullscreen (creating a new space) or just take the whole window.
It will be extremely handy to show the designs fullscreen, without all the tools and stuff around it. As mentioned by another user here. The main issue is with laptops, smaller resolutions; and projectors. Once we enter a meeting room, the quality is different, the abilities are different, and the way things look during the presentation is different. Having the full screen option will allow us to continue using Zeplin for one extra purpose. Right now we'll move away from Zeplin for presentations, as long as fullscreen option is not available.
This is possible now (2018) on the Zeplin Mac app. But my dev team (running on Windows) use Zeplin via browser, and the fullscreen feature isn't available yet there.
Zeplin will be user for (agile / scrum / review) presentations. It will be handy when designs can be shown fullscreen, without all the tools and stuff arround it.
Did you try top left green traffic light? is it what you mean?