Where do summoned monsters come from and what are they doing before being summoned?

[Epametheus]

Are you sure about this? I know that the descriptions of many outsiders observe -- or at least used to observe -- that they're lothe to use their summon whatever ability because they don't like incurring debts.

If the creature they're summoning isn't real, why should they worry about being indebted?

Hold over from 1E and 2E, when the creature was really called there. And maybe 3.0E, for that matter. Especially from 1E and 2E, when summoned creatures could summon more creatures and make a HUGE force in short time.

Of course, if a gelugon summons another gelugon, and the summoned one gets killed and has to reform, the summoning gelugon has some explaining to do when he gets back home.

Now, the summoning monster usually calls in lesser beings, so I don't know how well the lesser beings can stick it to their summoner. Just about any devil that gets called in by a Pit Fiend is gonna have to just suck it up and say "Yes sir, how may I help you?" But, if the Pit Fiend calls in another Pit Fiend, then he's bossing around one of his equals while the Summon effect lasts, and he's gonna need to show his appreciation for this favor later.

Something about how the Summon spells work brings the subject creature in fresh, and aware of the enemies of its summoner. There's nothing to indicate that a summoned Vrock would be able to attack the allies of its summoner, even if the summone was unable to order it not to.