They literally give you a 50% discount on that prison time by default and the rest you are released on probation, miss appointment or any crime and straight in front of a judge and can easily end up serving the rest of the sentence.
Sadly this whole automated 50% discount upon your sentence has made many people despair at the whole system and often see headlines of some heinous crime and how they are out after a few years.
Of course this whole process was from what I can tell a accounting way to cope with prisoner numbers and with that, curtail building more jails.
But many sentences are a joke already in the public eye, without the addition of some automatic 50% discount.
Today, they are trying to end that 50% discount for certain types of criminals - terrorist types being one and in the UK, been two well news instances this year of criminals of that category being out early and committing violence that in the first instance, led to deaths.
I will also add that many career criminals know the legal and law system better than those that enforce it and with that, know how to game the system and how to play it. With that personally I have no faith in our police at all, though that is based upon experience of drug dealers moving into the flats below and the police being beyond useless, even with hard evidence and literally passing on details of those who informed upon them onto the criminals - be that having a word, passing on statements, lapping up their lies.
One case, they called round to raid the place and knocked on the door whilst the gang was there, they were made to wait 5 minutes whilst the gang flushed the heroin and crack cocaine down the toilet - took 3 flushes to get rid of it. Then they let them in, surprisingly they found nothing.
I literally had to take the law into my own hands in the end and built a contact microphone and wired up the walls and recorded their activity and literally blackmailed them to bugger off, I then got evidence against the corrupt police and had a wee chat and they are now no longer with the police.
I tried all the legal avenues and did all the right things and got utterly and totally shafted/ignored and frankly after 50 years, utterly lost faith in the police in the UK these days. Which still saddens me and brings a tear to my eyes. I won't even touch upon the health impact of noisy neibours and the associated antics of drug dealing but let's just say, PTSD comes from many forms.