My advice to write thank you notes is not because i think it will get you an admission to a program. It is just the way I was brought up. We write thank you notes for everything. It only takes a second. It is usually much appreciated by the recipient. And it is just a nice thing to do. I see no reason why not to do it.
In the case of the MT process however, it is another positive way to remind auditors of who you are and when they saw you, especially if you can find something relatable from your time with them in your audition to share with them. In an increasingly large pool of applicants, the more you can remind them of who you are the better.
I am sure many students have gotten in great programs without writing thank you notes. But in a process where there the odds are so slim to begin with, I am all for giving each student every opportunity to put their best foot forward. I do think it is much better to err on the side of writing a note than not.
It’s a simple thing to do. But of course, to each his own.