Nutritional yeast is a yeast that is a dead yeast, so it won't rise your bread like baker's yeast would. But it will add a lot of nutty, savoury, cheesy flavour. I always look for fortified nutritional yeast whenever possible which will have vitamin B12 in it (which is important for vegans). It's also loaded with protein (2 grams per tablespoon) so it's an easy way to sneak more plant based protein in.