What can you do? You can order your bound outsider around, within the limits of the service you've demanded from it. (Which may well be simply "Accept my orders". You can cast spells on it, good and bad (though see below). But you can't order it on suicide missions, and you can't demand it do things it cannot do -- "Impossible demands or unreasonable commands are never agreed to". A called creature is not a summoned monster. You can't send it down the corridor to set off traps, nor can you order it to heroically hold off the demi-lich for a couple of rounds while you make your escape. It gets to protect its own life and continued existence, above any orders you might give it.
In terms of fighting for you, I would say that you can order it into combat against creatures of a lower CR, or more generally into combats where it's not at serious risk, whether because it's fighting alongside you and your party or for some other reason. But the RAW implies that there is a point where combat becomes "unreasonable", whether because the creature is badly injured or just because it perceives that its life is at serious risk. At that point, self-preservation kicks in and the creature seeks to flee. It is still bound to service -- "never agreed to" does not mean "breaks loose". But it's not going back to that particular fight, or at least not until things change to its advantage.
Finally, you can't order the creature to take actions that are obviously inconsistent with its nature or its alignment. The planetar just isn't going to massacre a bunch of paladins for you, amusing though the notion may be, and the azata isn’t going to help you enslave a bunch of people. The service you require may be difficult, unpleasant, and even somewhat dangerous, but it can't be something the creature would regard as morally abhorrent. That's "unreasonable" and it's not going to fly.
What can it do? The creature can still use all its SLAs skills, feats and abilities. And it will, for its own motivations and purposes, unless you specifically bind or instruct it not to. A succubus may use her Suggestion on your fellow party members. A shadow demon may possess an NPC. Devils will want to tempt people to wickedness. Daemons will want to hurt and kill people; fire elementals will want to burn stuff; angels will want to help, heal and rescue. That's their nature. You'll need to keep them on a short leash.
And, of course, the creature may well resent being bound, and may connive at your downfall and destruction. Note that called creatures get to use their SLAs and skills; a conjured devil can use Bluff to lie to you, Sense Motive to figure out what you really want, and so forth. The brighter ones are perfectly capable of pretending to be fine with the situation while quietly plotting something truly horrible for you down the line.
One way to think of this is as something like a hierarchy of motivations. Remember Asimov's Laws of Robotics? Something like that:
I. A bound creature will act to preserve its own life and will act consistently with its alignment.
II. A bound creature will obey the terms of its binding, except where this directly conflicts with Rule I.
III. A bound creature will seek to carry out its own agenda, except where this directly conflicts with Rules I or II.
Enchantments and other tricks. An interesting question is whether you can cast spells on your bound outsider -- Dominate, say, or Geas/Quest -- to make it safer and less troublesome. I'd say you can, but you can't command the creature to fail its save and accept your spell. That would be pretty obviously "unreasonable". You could even argue that being Dominated could potentially endanger the creature's life and/or force it to act against its alignment, and thus an unsuccessful attempt to cast Dominate would break the binding right there. I think that's an extreme interpretation, myself, but discuss this with your DM in advance. Certainly any attempt to Dominate or otherwise enchant a creature is likely to ratchet its resentment factor way, way up.
Does anything break the binding? The RAW doesn't mention anything, so I'm inclined to be conservative on this point. That said, I would say that if you attempt to kill the creature, either directly or by ordering it into a near-certain-death situation, then that would probably do it.
