I understand filing one gets you an earlier filing date with the USPTO ... but are there any other benefits? Are there any downside effects to filing a provisional patent application?

Great question! I will do my best to answer, but I'm sure there are several great people in this community that we could benefit from hearing from too!
You are correct in your assessment. Additionally you are able to put the label patent pending on your product potentially deterring competitors. It also will allow you to license to many companies if you intend to. Then you can use the revenue you make from the license to switch to non-provisional. Good luck!