I have developed hoarding tendencies that I caught before it got too far out of hand, but only just. I found myself buying four or five of anything I liked. I live in a tiny space, so it doesn't take much to make it cluttered, but I am tolerant of much more clutter now than I was even 10 years ago, when I kept my house pretty neat. But I don't have temptation to get more pets, for example, and I've stopped buying more than I need at the moment.
I think it is a way to insulate yourself from people. If your house is always a mess, you can't have people over. And if you have everything you need in your house, you don't need to go out where people are.
I think our whole family has hoarding tendencies, my sister has it in extremis but it is problematic really because she is also an impulse buyer and engages in way, way too much in the way of retail therapy.
Myself I buy and hoard books, way too many of them, although I think I could part with most of them I would still want to keep a core collection and I know that it would be difficult to make choices. A lot of my books are to be read books but they are also books which for some reason I've bought with a view to keeping until they can be read, as opposed to simply saying, well, that will be available to buy when I've the time to read it. So it is a kind of hoarding.
My mum and dad have definite hoarding tendencies, I think its more to do with being from an era when things where worn out or less disposeable, when I put together collections of books to dispose of at the charity shop or sell or give away my mum will always take some out of it and keep them.
Oh, the bus comment reminds me... There is a guy in our neighborhood who is likely a hoarder. I don't know if anyone else has seen this type of behavior, but he hoards firewood. We recently caught a glimpse of his back yard (his fence was broke and falling apart), half of his backyard was piled about 5' high with firewood. He keeps it in his driveway, along the side of his house and in his backyard. We used to have a woodpile in the backyard and it took us about 10 years to go through all the wood... I can't imagine how long it would take to go through all that he has collected.
He's also got a school bus that he keeps various things in... It's currently also doubling as part of his fence.... We're pretty sure he's an alcoholic as one day when we walked past you could smell the liquor on his breath when he said hi and tried to chat with us...