Depends on the weed. You can cut multiflora rose within three inches of the ground a couple of days before the flowers open, and it will expend all its stored root energy throwing new flowers up, and then you cut it again just before the seed sets, and it’ll kill it. If you don’t hit that schedule, though, you can cut it a hundred times and it’ll just grow back.
It’s pretty much always best to pull weeds up by the roots. Just be careful since some of them have extremely noxious sap (like for example, poke weed and wild parsnip) that you really don’t want to get on you.
Most weeds are weeds because they’re hard to kill and grow in the wrong place; otherwise, they’d be wildflowers. 
