I messed with this a bit and found fbdev forces even gpu accelerated video decode or rendered apps (e.g. even terminal text these days) to go through the CPU/RAM copy path whereas a lightweight graphical setup (like a minimal sway with a full screen terminal window open) is zero copy. Minor thing, but I'll gladly trade a little RAM for some battery life + simplicity if I ever do need to open something actually graphical on the machine.