I'm glad you found the forum useful and you will be in good company, as most of the active users seem to be here for SO. It's a growth industry and most probably a consequence of exposing our society to 24/7 internet pornography. The effects of which, are not yet fully understood or appreciated.
As someone who had no previous contact with the law, I was also shocked by the PPU turning up, unannounced, on my doorstep one day and wondered what I had done wrong. I later learned that this is just, what they do. It's partly about information gathering, checking for 'lifestyle indicators' of risk, and funnily enough, about building rapport with the offender. They don't tell you that you are under no legal obligation to speak to them, since that might encourage people to just say 'no comment' to all of their intrusive questions. But, I concluded that being open with them was the best way to build a positive relationship. The same goes for probation. It doesn't always guarantee that they will treat you fairly, but hopefully they will.