To trellis or not depends on whether the seed packet states your bean variety is a pole / runner / vining bean versus a bush (sometimes French) style. Pole beans need a trellis, bush beans do not. I have lost track of which varieties I have grown on which style of plant, but the drying beans tend to mostly be bush style and they all work well according to the planting pattern for their habit as indicated in the plant spacings in the FAQ.

Here is a link that might be useful: GW Sq Ft Gardening FAQ