The only sensible reason for using a low-end card instead of the iGPU is if the card gives you a healthy amount of dedicated VRAM, but unless it's got at least 2GB VRAM there's no point. If it's only got 512MB VRAM it's hardly worth using, your iGPU could probably beat that with the amount of system RAM it's configured to use.
I'd only use it as a "stop gap" if, for example, the system had no integrated graphics adapter.