Hi Brian,
If you use default-information originate always then OSPF advertises a default route, even if you don’t have a default route in your local routing table. The “problem” with this is that you “attract” traffic to destinations that you don’t have a route for. In reality, you probably use this on some edge router that is connected to the Internet and you have a default route pointing to your ISP.
If you wonder about something like this, instead of trying to “think it through”…boot up some routers, configure this on OSPF and see what happens when you send a ping from another router that receives that default route. Seeing it in action lets it sink in your brain 10x faster than trying to brute force things in your memory 
Rene