When you cast your rings you have the option of having a safety mold made of your bands. Then, if your rings are ever lost or stolen they can easily be recreated by a caster. When you make your own rings they really do become irreplaceable, since no store bought ring will ever compare. For only $45 per mold some have said that they are worth their weight in gold.
The mold is also a great option if you think that you might want to recreate your ring in an other metal down the road. Wedding planning is expensive and precious metals aren't cheap, that's for sure. So some people choose to start will silver rings then have them cast in white gold or platinum later.