It's 'useless' trying to change her mind. = It's 'useless' to try to change her mind.
Drugs are 'useless' in treating the condition.
I made a 'useless' attempt at fixing the leak.
(..) Oh, no. Toothless, what are you doing? We need her to like us! And now the spinning. Thank you for nothing, you useless reptile. OK, I am sorry! I'm sorry. Just get me off of this thing. All right, I admit it. This is pretty cool. It's amazing. (..)2010 How to Train Your Dragon