Admin's are regularly presented with operational challenges. One of the most common one is to optimize content database size. We do not want to have large content databases as it becomes difficult to backup/restore
If possible, move site collections between content databases so that the size is manageable.
Step1: stsadm -o enumsites -url "web app url" > sites.xml (Concat results to an xml file.)
Step 2: stsadm -o mergecontentdbs -url "web app url" -sourcedatabasename "source db name" -destinationdatabasename "destination db name" -operation 3 -filename "sites.xml"
Step 3: IISReset /noforce