Vlad They still take up space. I prefer the behavior of Firefox and Chrome with pinned tabs. Before I moved to Safari, I used pinned tabs all the time. Having them show up in every window is not helpful for me. I effectively gave up pinned tabs in my move to Safari.
Some context: I'm a developer. I have three screens and make use of Spaces. Typically, I have 7+ browser windows open at a time. Each browser window/screen/space represents a different context (email, communication, primary project, secondary project, research/documentation, scratch pad, entertainment/distraction, etc). I used to have pinned tabs in the browser windows of each of these contexts. With Orion/Safari, this would mean every window could have up to 10 pinned tabs, most unrelated to each other. If I'm in a specific context, I know what each pinned tab means. However, if the pinned tabs show in every window I have to think a lot more about which pinned tab I need. Suddenly this feature just causes more mental work than without it.