First of all the service broker is intended for handling messaging between two or more instances. Have a look at
SQL Server Service Broker[
^]
If you just need to do background calculations, why not utilize
SQL Server Agent[
^]
Another thing is that enforcing business rules should typically be done immediately when the data is modified, preferably inside the modifying transaaction. If you postpone the running the logic, you may easily end up in situations where the database contains illogical or even false data.