[Q] Table aliasing

Hello.

I have a noob question about table aliases in SQL.

Suppose the following query:

SELECT *
FROM deal
WHERE
deal.id IN (
SELECT DISTINCT deal.id
FROM
deal
JOIN partner_share ON deal.id = partner_share.deal_id
JOIN partner ONshare.partner_id = partner.id
WHERE
partner.team_id = 12345
AND (
partner_share.type = 1 AND deal.external_id IS NOT NULL
OR partner_share.type = 2 AND deal.external_id IS NULL
)
)

As you can see, the IN (...) references the deal table too.

My questions:
* Should I alias one of the references to deal?
* The above query works the same both with and without an alias, so is it simply
a matter of taste / good practice?
* Where can I find more info about this, i.e. when the alias is mandatory and
when it is only a convenience? I've scanned through

http://www.postgresql.org/docs/9.1/static/queries-table-expressions.html

but it only mentions that subselect in FROM must have an alias. I would like to
know about IN (...) and EXISTS (...).

Thank you,

L.