Planks can be new, strong, and sturdy. Or they can be old, loose, rotten, and crumbling. If you find a loose plank on your deck or on your staircase, it might be dangerous. Or might be a good hiding spot for a secret treasure.
Finally, "plank" can also mean "plop" or "plunk." If you plank your money down on the counter, you're plopping it down in a loud way, as if it's a slab of wood that you're dropping onto the counter. It's kind of rude.