Of course they wouldn't cut logs or post with it but saplings to weave in between the post that's likely.

I also am not a historian I work construction. The Romans always fortified the camps they made and a short sword could be used to aid in digging cutting post even firewood if needed. So I see it more as a multi purpose tool. Also metal was not just left after a battle it would have been collected and reused.

Besides most castle walls were brought down by undermining.

Did you even read the original post. Its about covering the walls not just the doors.

This post is about covering castle walls with metal to make them stronger they had arrows.

It still has to be smelted and forged and at the time in pieces small enough to be man handled. Even during the American civil war when metals were easier to source no one tried that because it had far more value used in other places in the fight. What would you rather have a four foot by 8 foot sheet of metal or an extra thousand arrows.

You have to consider that all metals at the time were produced by hand and forging large sheets would have been next to impossible. Much cheaper just to go thicker.