There are a lot of benefits in having separate content database for each site collection, especially in term of storage management and migration. But I can’t find a place to specifying that when creating a site collection in Central Admin UI. But this can be done via stsadm commands as below:
stsadm -o createsiteinnewdb -url http://webspinners/dept/hr -owneremail SharePoint@webspinners.com -ownerlogin Webspinners\SPAdmin -sitetemplate sts -title “Human Resources” -databaseserver “SERVER5″ -databasename “HR Content Database”
If you need to know more about this. I found below blog entries to be very informative.
In summary, in our cases, we find it very helpful for scaling to multiple database servers, it simply involves moving content databases to the new server and updating the location in SharePoint.
Also, as another user pointed out, WSS databases are “self-leveling” like water. If you create a new content database, it has 0 sites. The next site collection you create will go there. So you can actually do this without the stsadm commands if you plan ahead.