Tim. I'm responding to your original question. Here are reasons to join a PRO:
1) You regularly are performing your songs live ( and can verify this). ASCAP has grants for which members who do this must apply each year. No guarantees are made that you'll get one, but at least you'll be eligible. I received such grants in the past when I performed my own songs live. I don't know what BMI or SESAC has to offer along these lines.
2) You have a release and you are the publisher. It's always a good idea to have your publishing entity affiliated with a PRO - and put it on your business card and any release.
3) If you want to take advantage of any of the services or programs that these PROs offer their members.