The AS Path
While the autonomous systems contained in the AS Path are not used in determining which path to use (i.e., the AS path length is a component of the bestpath calculation, not the AS Path itself), and it's not a good idea to use the AS path to set policy based on the existence of some distant autonomous system, there are still some common policies that are implemented based on the AS Path.
Remove Private AS
One common method use to dual home to two different service providers (or even to dual home to the same service provider) is to use a BGP private autonomous system number to peer to the service providers and let the service providers strip the private autonomous system numbers out of the path before they send them to their peers. ...