It will help alleviate some work load on you or processor, so its not having to run the PC and display, and give more options some motherboard's don't have like HDMI, DVI-I/D and VGA. But for gaming this card is going to struggle to give playable fps, and even then everything will need to run at low.
I suppose one advantage is you can still play older games with no issue, so for a nostalgic gamer who say likes to play the first Command & Conquer or the tycoon games or any of them(i did not say retro as i don't class these as retro) then that's fine but for newer games i don't think you will have much luck I'm afraid with out upgrading both power supply and GPU.