Comment by singron

I also wasn't there, but I think this actually wasn't to help authors and instead was a workaround for the warts of SQL. It's a pain to write

    SELECT * FROM (SELECT * FROM ... GROUP BY ...) t WHERE ...

and they decided this was common enough that they would introduce a HAVING clause for this case

    SELECT * FROM ... GROUP BY ... HAVING ...

But the real issue is that in order to make operations in certain orders, SQL requires you to use subselects, which require restating a projection for no reason and a lot of syntactical ceremony. E.g. you must give the FROM item a name (t), but it's not required for disambiguation.

Another common case is projecting before the filter. E.g. you want to reuse a complicated expression in the SELECT and WHERE clauses. Standard SQL requires you to repeat it or use a subselect since the WHERE clause is evaluated first.