ios default routes; CCNA related question

now that i understood it, let me try to explain my interpretation of it:

say you own two subnets and you'll have to configure routing between them. if you only set up the routes between these subnets, routing will be done between these two subnets only, which is rather static (assume simplified that you could even use static routes instead of a routing protocol). if you want to send data to other networks you don't know anything about, you'll have to set up a default route to some type of gateway which then routes to these networks. this default route, once configured on a gateway will be distributed via routing protocols to the other network, so the other subnet can use this route to "dynamically" send packets to unknown networks.

hope this helps (and was correct