OIDs (Or: another RTFM question?)

Yo!

Browsing through the online docs, I see the special columns documented
in http://www.postgresql.org/idocs/index.php?sql-syntax-columns.html .

But I'm missing discussion about significance of the oids - something
along the lines of 'Creating tables WITHOUT OIDS does *not* safe any
disk space, but does <give you what?> at the expense of <what? being not
backward compatible, I guess>.'

Such documentation seems necessary to me, since pg creates tables with
oids per default (does it still?), but intuitively I feel this somewhat
silly - as oids are obviously optional, why have them built in?

(I'm sure these issues have been beaten to death when the WITHOUT OIDS
feature was introduced, but I couldn't find the relevant discussion in
the archives. Pointers welcome.)

cheers
-- vbi

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