There are three cases that must be considered for your question. I will answer your question directly first, and then mention the other two cases.
Think of “default-information originate” as a safety check. Suppose there was some careless BGP admin that told a router to redistribute some other protocol’s routes into BGP, say EIGRP. If that admin didn’t use a route-map or some other filter, and he didn’t think about that EIGRP was advertising a default route, the consequences could be really bad. You might not want all of your BGP peers to learn a default route from you! As a precaution against this, if you redistribute other routes into BGP and you really intended the default to be included, you must additionally type in “default-information originate.” So in other words, “default-information originate” really has no meaning with BGP unless it is paired with a “redistribute” statement.
(config-router)#neighbor 18.104.22.168 default default-originate
What this does is advertise a default route to a specific neighbor. BGP will do this even if it doesn’t have a default route itself (so this is an exception to the rule where you can only advertise networks that are in your routing table).
The last case is advertising the default network explicitly like this
(config-router)#network 0.0.0.0 mask 0.0.0.0
Doing this will cause BGP to advertise a default network, but only if you already have the default network in your routing table.