In my experience it is helpful. When I was doing my wifes sponsorship, i got her GCMS notes after she got PR. In it, I clearly saw a note that said the letter from the lawyer had made a difference and bumped up her processing to urgent. He had writted a letter with reasons as to why the delay was impacting us. Not sure if I had written the same, it would have had the same effect, especially because they know the language to use.