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Interesting -- didn't know it did this

One way I've seen it used is when you need to order by all or nearly all of the columns in a select statement. Sometimes

select a.1, a.2, a.3, ... a.10 GROUP BY 1,2,3,4,5,6,7,8,9,10

conveys the intent more clearly than listing out all the column names

It is also very helpful to avoid re-typing expressions.

select a || 'baz', avg(b) from foo group by 1 order by 2;