>>723338949
if you have a PC from any gen after like a 1050ti it's not something you'll notice. what fullscreen does is switch to exclusive rendering mode, which means it doesn't render anything but the game while you're in the game, but when you tab out it has to switch to rendering the desktop again which causes lag, and so on and so forth going back and forth from game to desktop, while borderless windowed is still full screen but without having that render lag/video output switch from tabbing in and out.