PROs/CONs to having separate BGP ASNs as opposed to having one larger BGP ASN?

Hey all.

I'm having a difficult time trying to figure out what the pros/cons would be to having one large BGP ASN as opposed to 2 or 3 smaller ones. A little context:

We have one site on the east coast that is one BGP ASN. Another east coast site not too far away (50 miles give or take) that is another BGP ASN and then a third one out west. We just had a discussion of potentially collapsing the east coast sites into one ASN and it got me thinking, what are the benefits to collapsing them? What are the benefits to keeping them separate?

Thanks.