unicode for database - best for overall performance?

i read in the below:
stackoverflow.com/questions/144283/what-is-the-difference-between-varchar-and-nvarchar

"ll modern operating systems and development platforms use Unicode internally. By using nvarchar rather than varchar, you can avoid doing encoding conversions every time you read from or write to the database. Conversions take time, and are prone to errors. And recovery from conversion errors is a non-trivial problem.

If you are interfacing with an application that uses only ASCII, I would still recommend using Unicode in the database. The OS and database collation algorithms will work better with Unicode. Unicode avoids conversion problems when interfacing with other systems. And you will be preparing for the future. And you can always validate that your data is restricted to 7-bit ASCII for whatever legacy system you're having to maintain, even while enjoying some of the benefits of full Unicode storage.
"

Can you qualify that if it is safe to allow nvarchar even when unicode is not used in the application, but may be better for overall system?

thanks.