shared content

I'm currently in the process of developing a site that I though may be a candidate for a multisite configuration, but I'm not certain. Basically I will ultimately be creating a number of subsites based on geographic location (something in the realm of how craigslist does it). There will potentially be quite a few nodes. Since individuals will come to the site to view info specific to a location, I though for the sake of database size, it might make sense to split it up. I guise to cut to the chase, I'm wondering what the advantages are based on my critera.