I think viewing websites in fullscreen or not greatly depends on what device you are using. Because of this, I think there are no general advantage or disadvantage, but the choice should depend on the device.
Here are my thoughts:
Firstly, immersion or distance.
- Working at desktop (and in a working enviroment) most people prefer a distant view, which gives you a mental distance either.
- And at desktop, you need to control all currently running applcations. Probably you like to have a glimpse to Outlook while working on
- Watching TV is fine for fullscreen. Here all attention is focused on the content and browser chrome or buttons would distract your pleasure.
- Mobile and Tablet aren't immersive by its physical size. I think immersion or distance aren't a point to consider here.
Secondly, it depends on how many and how large the screen are.
- Working with 2 monitors fullscreen isnt't useful if you need to see two programs simultaneously.
- If you have a 21 inch monitor at your desktop, you will be blown away by fullscreen. As a rule of thumb the diagonal size of screen is the ideal viewing distance.
- Tv-Screen lack of resolution, a decent reason to avoid loosing pixels by unnecessary chrome.
- Mobile and Tablet usually have small physical screens and its wise to go fullscreen in order to save space.
Thirdly, technical limitations
Windows just allows you to go fullscreen at first monitor by technical limitations of DirectX, which is forced by graphic cards.
TV introduced In-Screen Views (2nd channel at a corner) just a few years ago and lacks of a usable input device to steer multi-tasking.
- Mobile were very limited by its CPU power, in its early years, and thus presented just a plain black/White pixel menu. Nowadays they are small computers though.
- And Mobile just introduced multitasking recently, so it wasn't possible to see two applications simultaneously.
- Tablet hasn't this limitation, because its brand-new. A technical limitation could be the size of your finger, forcing GUI elements to be as large as possible.
Fourthly, the history and habit
- Desktop is used to be windowed (if you just reckon its GUI)
- TV is used to be fullscreen.
- Mobile is used to be fullscreen.
- Tablet is used to be fullscreen either.