You summed it up nicely. Besides the amount of time you are wasting, you can use it to do something productive. You are not making money nor even having entertainment.
You know some people have nothing to do. If someone does not have any special skills to work, you can take me as an example. I am just an average dude who does not have any special skills, so it's hard for me to get a job. While I look for a job, I can spend time on casino chat if I want and hope to make some money. That was when I was a student and had nothing to do. But as I said, I was not profitable for the casino.
I've been doing the same thing and yeah, you're right it's a total waste of time, especially if you don't get any chat rain of what you want. But if you're lucky enough to get some $ in chat rain and turn it into a decent amount, that's a different story. I did manage to withdraw twice from some online casinos without making any deposits because of the chat rain. So it doesn't always a waste of time for me.
A couple of months ago, a high roller dude rained 500K plus on BC game chat, and each player received 10K USD. He did this a couple of times. Imagine you are in a casino chat and get 10K rains. That is a life-changing amount in third-world countries.