Scenario: DBA1 left the company and never removed him/herself as the owner of databases all over the company. You are DBA2 and just got hired to replace DBA1. They plan to disable DBA1's account tomorrow.
You can either walk through every database on every server or connect to each server, choose your desired new owner login (in this case I choose SA) and run this script to save the day.
In later version of SQL Server you can run this against several instances at one time.