I think it’s a great way to practice your inner, psychic hearing. I tend to write whatever comes to mind when I’m journalling, and automatic writing in a ritual has a very similar feel to it. I think it helps you let go, like you said, and get into the flow of receiving without getting in your own way. After doing this a lot, I noticed that spirit messages have this sort of quality or feeling to them that’s distinct from my own thoughts, like something you tap into in your mind.
I can communicate with spirits now without the need for writing, but I still do it more often than not. I like having a verbatim record of what the spirit said, and it does still help keep the connection strong and free from distractions, especially if I happen to be feeling a little drowsy or low-energy late in the night or early morning, keeps me from nodding-off with my eyes closed.