This is a bit like asking 'How long is a piece of string?' in that it is different in every case and in every set of circumstances.
You and your representative should discuss both what outcome you want and what you would be prepared to accept as a compromise.
You should bear in mind that your representative does not have a magic wand.
Just involving your representative does not in itself guarantee that you will get what you want.
If management is able to concede what the representative is saying on your behalf or if you have discussed all aspects of the case and have reached a compromise then it is often acceptable to settle the case and that should be an end to it.
If you and your representative are unable to agree with management a suitable outcome, then you will have to discuss the case again.
Sometimes your representative will be able to obtain more advice from his/her full time officer or or other experts within PCS.
In these circumstances they may be able to discuss with you what the next steps might be.
Sometimes it means that you will have reached the end of the road with this case. Other times it may well be possible to appeal to a higher level of management, or even to take legal action.