You know, if I were somebody else I would make this a nice shiny meta full of Thinky Thoughts and people would link it and stuff. ;-) As it is, it's a random brain-babble.
Anyway: when you move back in with your parents and siblings, most of whom (including you) are not particularly organized, you start thinking about Stuff. Categorizing, cutting down on, and putting away Stuff.
I've read a good many books about organizing, decluttering, dejunking, simplifying, and all those other things. They all have different systems. Some of them are sensible, IMO; some are not ("if you buy a book, you must get rid of a book!" *ka-pow*).
I, too, have a system - of sorts. My thought is that all the Stuff under one's ownership falls into three categories and a sub-category:
Past, Present, and Future. (And Timeless.)
* Past stuff can range from old candy wrappers to bronzed baby shoes to high school diplomas.
* Present stuff is stuff you're using or working on right now.
* Timeless is a subsection of Present; it's the stuff everyone needs to have in some form, like a bed or a drinking cup.
* Future stuff is stuff you plan to use someday. Having it around now is a way of directing the future toward the way you want it to be - a popular example is an exercise bike. (I've got a weakness for pretty fabric, myself. I don't sew, but I could.)
Anyway! Past stuff is the most common category for professional organizers to attack, because it's easy to say "why are you keeping all this old stuff around? you should Look to the Future!" But it's not necessarily bad to have Past stuff (or Present stuff, or Future stuff). It's all about balance. You keep the stuff that makes you happy and ditch the rest.
Present stuff... is mainly a problem if you're distractible, like me. You get umpty-billion projects going at once, but because it's all Present, you don't have a set place for it. The solution to this is basically designating places and making sure you have enough space to store a new project before you start it.
Timeless stuff shouldn't be a problem, really, unless you have a tiny apartment. It's more like the solution to the problem - if you're totally overwhelmed in clutter (and I'm talking to myself as much as anyone here), you can start with using just the Timeless stuff and boxing the rest, then slowly seeing how much else you want to work in.
Future stuff can be a problem if you try to prepare for too many possible futures at once, or try too hard to bring the future into the present. (Like if you have fruit bowls on the side tables to encourage your family to eat more fruit; at some point, you just can't keep all the fruit fresh. I actually knew someone who went overboard that way once.) Again, the point is balance. You don't say "never prepare, just be Spontaneously Flexible!"
Aaaand... I am fail at conclusions. Which is why this is not a shiny meta. ;P