Well, I wouldn't put a bed quilt on a picnic table, but I have made quilts specifically for picnicking that are used on the ground - I wouldn't care if those were used on top of a picnic table.
I don't know if I'd use a star block quilt for that purpose though...I make scrappy crazy quilts for that use instead. Triangles are still tricky for me so I don't do those except for special quilts! LOL