Good article and great topic. I'm a big fan of computed columns so it's nice to see a detailed article on the topic. I would warn, however, against using a T-SQL scalar UDF for a computed column if performance is important. Once a scalar UDF's (pre-SQL 2019) becomes part of the table queries that involve that table will become slower. For starters, queries involving that table can no longer get a parallel execution plan even when that column is not referenced! Even index rebuilds must be performed with a serial plan. Based on my testing, non-inline Scalar UDFs bring these kind of problems when used for computed columns or as constraints (Check & Default). Note these two articles by Eric Darling:
Another Hidden Parallelism Killer: Scalar UDFs In Check Constraints
Another reason why scalar functions in computed columns is a bad idea
Again - I enjoyed the article and am looking forward to the next one. I'm not being critical of it in any way, I just wanted to make people aware of the performance implications of using scalar UDFs for this. A correctly developed CLR, on the other hand, does not have this problem. Fortunately, too, SQL 2019 adds inline scalar UDFs which solves this problem on the T-SQL side.
"I cant stress enough the importance of switching from a sequential files mindset to set-based thinking. After you make the switch, you can spend your time tuning and optimizing your queries instead of maintaining lengthy, poor-performing code."
-- Itzik Ben-Gan 2001