Errors occur in tooth number in the ledger frequently as the front desk doesn't always understand things going on in the op. When having to do an adjustment to correct a tooth number and then rebill it correctly, you have to connect all the dots in the ledger to figure out what happened later. If the note section was left open, you could invalidate the procedure and make a note as to why the correction is being made, without having to search through the ledger as to why.