These are common garden spiders, not harmful at all to humans and are, indeed, beneficial because they eat flies, gnats, mosquitos, etc. Their babies over-winter in sacks in the webs (after the female - shown here - dies) and then break out in the spring. That's why it's uncommon to see them do it...old web and that sort of thing. They love gardens and sunny spots. Call them Charlotte and love 'em!!
Jan in VA