A quad core (4) will decode video, but will result in stutters compared to something like an 8 or 16 core CPU when playing back video with no Hardware/GPU Acceleration enabled. Hardware/GPU Acceleration is much more effiecent in handling these type of tasks.
Also if you’re doing other things in the background while trying to play video, will impact perf here, if your browser is trying watch a youtube video with Software rendering.
I would enable it yes, but only if it doesn’t cause any breakages, or any graphics artifacts. Only time if recommend if you disable Graphics Acceleration is if the GPU drivers are buggy or just too old/unsupported.