Yes, there are those who don't want to come back into society in exchnage for a warm place to sleep. But there are others who due to circumstances have lost their home, their work, don't have family and simply cannot afford to stay in rented accomodation and prefer to sleep "rough" as long as they can in the hope that they get another chance tomorrow because going to shelters mean in a way accept life on the street, at the bottom of society, they get registered and regulated etc., somnething you need time to accept.
Especially in times of recession, lots of people loose their home, people who never knew how homeless people live and have no idea to inquiry where they can find help for fear to be marked fro life. (I read in a book taking place in the Uk that it is impossible to remove certain information from your social services papers, even after you got out of trouble and no longer need help. Not sure if this is true, but go figure! )
So when Catherine goes sleeping rough in order to help Centerpoint getting more attention, she does two things: highlight the fact that there is Centerpoint at all and that's an acceptable way to look for help. But much more important is highlighting that sleeping rough as a woman is different than doing it as a man. Sure she'll be protected, but I guess her protection officer will only intervene if something threatens to happen actively, not clearing the place in advance and cordon it off with the help of police collegues. It will be an important experience for Catherine and I wonder if she will sleep at all for feeling insecure and threatened at night, outside, on a pavement in London. I'm sure it will be an experience that gives her an insight into the fact that poor women are at the bottom of it all.
And that might change her whole view on life and on her duty to help. IMHO, of course.