It's a real shame that and other MS documents don't actually cover the major problem with computed columns as Brent Ozar did in the following article, which also has a pretty good suggestion for a fix...
RBAR is pronounced "ree-bar" and is a "Modenism" for Row-By-Agonizing-Row. First step towards the paradigm shift of writing Set Based code: ________Stop thinking about what you want to do to a ROW... think, instead, of what you want to do to a COLUMN.
"Change is inevitable... change for the better is not".
"Dear Lord... I'm a DBA so please give me patience because, if you give me strength, I'm going to need bail money too!" Helpful Links: How to post code problems How to Post Performance Problems Create a Tally Function (fnTally)