well, it cuts down to the customer routing.. because having different ASs will definitly change his routing, but let's say that that doesn't matter.
giving each site a different AS will make the configuration easier because this will be the default behaviour of BGP.. which is good in some cases..
of course when it comes to having the same autonomous system in multiple sites, or in a hub and spoke topology. it will surely increase the complexity of it as one mistake can really spin the network around.. but i'm sure as you might know that you can use SOO to prevent loops from happening..
it really drops down to the network itself more than anything..