The only advantage I can think of would be that you didn't have to stop taking video to take a photo. Even that, though, can be surmounted--most consumer and some prosumer Canon and Sony video cameras can take a still while taking video, as long as the video isn't at the highest bitrate setting. So for example, the Canon HF S30 can shoot a 8MP still while shooting video without interrupting the video stream.
Disadvantages: low resolution, high likelihood of motion blur in any individual frame (unless you're shooting with a really high shutter speed, which is unlikely UW since you have less light to play with), less depth of color in any individual frame than on a regular still image...the list goes on
Can't disagree with anything you say.