Traditional casino games are more for funs and less for earnings.
This depends on where do you play and how often do you play poker
If you play just within your neighborhood then I think that can't sustain your daily expenses since it's done usually during free time, but if you are talking about those poker pro's that you see in TV, well maybe yes It can help you go through your daily expenses. But isn't it that they also have managers that get's cuts from their winnings?
yes they do have a manger to take a cut but they still earn a whole ton of money. And with sponsorship etc. The monthly income can be quite huge!