Inside SELECT()(-ish) functions, that have their own frames of reference,
[_THISROW] gives you direct access to the row from which the SELECT() was invoked. I recommend always using
[_THISROW] if you intend to reference the enclosing row, else you run the risk that an identically-named column will be added to a scanned table and produce ambiguity and confusion unexpectedly.
Outside a SELECT()(-ish) function,
[_THISROW] is equivalent to dereferencing the current row’s key column. So if your key column is RowKey,
[RowKey] are equivalent.
SELECT()(-ish) functions are: FILTER(), LOOKUP(), MAXROW(), MINROW(), and SELECT().