SQL Server : Is it necessary to disable SA user for security issues?
Renaming or disabling sa account is just part of the story. 

There is no drawback if you disable sa account. 

It means if you have databases whose owners are sa, there isn't a problem. 

System databases like master, or tempDb require that sa be the database owner. 

If you try to change the owner of system databases you will receive 15109 error. 

Similar situation is with SQL Server Agent jobs, owned by sa. They won't fail, either.

IMO good practice is to have at least one account enabled with sysadmin role.