it's pretty simple, you tag routes so that you can filter or manipulate them elsewhere. Pretty common to do in enviroments where you have multiple entrance points to routing domains or have multiple routing protocols running and multiple redistributi...
furthermore, depending on who the two providers are, you may need to add a few more prepends to the route-map. I assume you are talking about prepending when you mention bogus entries :)
The easiest way to see how your prefixes look upstream is to login to a free route servers / looking glasses and see. Go to www.traceroute.org, there is a huge list of these so you can see if your prepending is getting dumped by the provider. Most pr...