They can be. However, look for large pins, pin on pin type, dangles, etc. Those are mostly AP or PP pins that Disney seeds the boards with. Even if they aren't stuff you collect, you might be able to trade them with others for things you do collect. We also used to use the boards to pick up the last 1 or 2 Hidden Mickey pins that were harder to find.
Once you see a board or two, you'll start to get a feel for things. And my trick is, unless it something you love and can have the CM pull right away, keep looking through all your time (it will go faster than you think). Put a finger on the two pins you want, so you don't "lose" them on the board, then when you hit the last 10 seconds, you can just say "these" and then the CM can pull them off.