rarely sufficiently covers the cost of living, though yes in some cases (e.g. if you get the top end of the stipend range from a rich university that also happens to be in a low-cost-of-living area).

terrible idea for someone who just wants to work (if you can get into a good grad school you can find some job that pays better and has better working conditions); conceivably not a terrible idea for someone with specific career goals who is trying to ride out some specific industry downturn.