If you have some site collections but your database grows every day. In  MSSQL size of database should be less than 200 Gb. So if your content database size less than 100Gb you can easily use only 1 database – it’s easier to backup and restore it.

But if your SharePoint starts working slow or size of your content database grows, I recommend you to create a new content database and move to it some site collections.

You can do it via PowerShell:

Move-SPSite http://siteCollectionUrl -DestinationDatabase DestinationContentDb

 

I recommend to move site collection to new content database using db_owner account or FarmAdmin account.

Steps before moving

• Get information about SharePoint content databases
• Determine SharePoint site collection disk usage
• Create a new SharePoint content database from PowerShell