Thank you!  I'm not exactly sure what you're wanting to know when you say you hope there's a purpose for the torment.  If you mean, why am I writing it...well, the idea occurred to me and I wanted to try writing it, because there's the potential for some good angsty, hurt/comfort scenes, and I enjoy writing those. 

Also, even though of course slavery is a terrible thing and a sensitive issue, as I noted at the beginning of the story, I'm not really thinking of Harry's case as a typical example of slavery, where one group of people subjects another out of their own cruelty or greed or desire to dominate.  Severus doesn't want to own Harry.  If there were a safe way to free him, Severus would do it in a heartbeat, and he's not going to intentionally abuse him, at least not physically.  Right now, Sev is still in his 'I-hate-all things-Potter' mode, so there may be some nasty verbal exchanges before Sev starts to warm up.  Anyway, though, to me, Harry's case is almost more comparable to someone whose life is drastically changed by some type of accident or the onset of a chronic disease.  It can be very harsh and unfair, and life is different afterwards, but it doesn't mean that the person's life is forever ruined and that they can never find any joy or peace again, either.  I guess I'm hoping, without trying to sound 'preachy', that the story can be life-affirming and give a message that no matter how bad things may be, they can always get better.

If you're wanting to know within the context of the story...the slavery spell will eventually lead to Severus and Harry becoming a family, and to Draco's redemption, too.

Now, about the Potter and Black lines and inheritance...I don't think it necessarily means the end of that.  For one thing, though I'm not going to take the story into Harry's adulthood and I want Severus to live a very, very long time and die peacefully of old age, there is the fact that once Severus dies, Harry will be free again (assuming Harry outlives Severus).  At that point, he would regain ownership of all his possessions. 

***Small spoiler for story ahead***

At a later point, Harry will say something about how he can never marry now, and Severus will reassure him that that isn't true.  He'll tell Harry that, though for ethical reasons, of course Harry should let a potential wife know about the slavery spell, it really shouldn't have a drastic effect on how they would live.  Harry may not be able to legally own things, but Severus gives him the freedom to use things however he wants, and he'll explain that among wealthy wizards who have family estates, it's very common for two or three generations to live together, so a potential wife could adjust to Severus having to live with them, hopefully.  Also, Harry's children would not be slaves and they could inherit anything Severus would want to give them.

Well, I've really rambled, and I'm sorry for that, but I hope I've answered your questions, at least partially.  Thanks again.