I don't think I've ever used a right join in a production query (perhaps a couple of times when I was doing some digging and it was easier), but I don't understand your statement. Left joins are insanely useful. For example, getting all the sales for a salesperson:

    select
        sp.Name,
        sum(s.Amount) as TotalSales
    from
        SalesPerson sp
        left join Sales s on
            sp.SalesPersonKey = s.SalesPersonKey
    group by
        sp.Name
    order by
        TotalSales desc

If you did a correlated subquery, it would take a ton of time to complete (`select sum(Amount) from Sales s where s.SalesPersonKey = sp.SalesPersonKey`), especially on large tables.

Left joins (and full outer joins) are plenty useful and I use them almost daily. Care to explain what you mean?