Not strictly a "leaving" issue but more an issue to stop you getting into prison in the first place. The judge can refer you for a Pre-sentence Report. You will see a Probation Officer just twice. Whilst protecting the public a Probation Officer is wanting to find reasons why you should not go to Prison.
Prison does not work so why send you there.
For Punishment of course, to set an example to others as a deterent and to protect the public. So you might not be able to avoid Prison but the Probation Officer is the one to help you.
He will want to know that you recognise that a crime has been committed and that you knew it was wrong. He will look for regret and a dtermination not to re-offend. He will also look for good reason why you should not go to Prison. Effect on your family, your health etc.
A Probation Officer knows that Community Service works better so you need to be fit to do mainly manual work and be willing to do it.
Whilst his report will not exactly say what the sentence should be, the Probation Officer will give an indication of his thoughts.
Until a few years ago Probation Officers were in every prison working with inmates. Recent changes mean that the old regeme of Prison Officers locking you up and the Probation Officer sorting out your problems have gone. Prison Officers now do both under the management of the Probation Service. Some inmates feel that Prison Officers now lock you up and leave you to sort out your own problems. It shouldn't be like that but it is.
However, a Probation Officer is still involved in sentence planning and your progress through the Prison System and transfer to less rigid regemes and prisons eg to an Open Prison.
The Probation Officer administers the HDC recommendation to the Governor and his panel. You might see a Probation Officer during the HDC process but for many first time offenders HDC is an automatic process.
The Tagging Period (HDC) and release on licence or Parole is managed by the Probation Service. You might be required to keep appointments to see the Probation Officer who will monitor your sentence.