No borderless changes the performance in BF4
No borderless changes the performance in BF4
Borderless typically causes a minor slowdown in performance across most games, though the impact is relatively small
Unless you boost the quality (borderless doesn't help), you won't see any drops.
Running in full screen keeps the GPU from rendering the desktop or anything beneath the game window, though this effect is slightly reduced. This is why I mentioned a minor decrease, which is generally small.
The GPU isn't rendering anything except the game in both settings. If you don't notice it, the GPU isn't displaying it, which is straightforward. You could mention that when a game starts loading and the GPU shows activity but nothing appears yet—it happens because it's drawing behind the loading screen, though the real reason is the CPU preparing the GPU's memory for the game.