I have moved house twice in five months. I am not done with the second yet. Due to condition(s), it will take time. I am still picking up stuff from other places. Some are boxes with stuff that hasn't really been used for many years. You know, the sort of "Good-to-keep" stuff or "If I throw this away now I will surely need it next week" or "This is very nice looking stuff that are stored away but some day I will put it on the wall". Maybe it will look nice in 20 years time, but probably not. Then there is also "I will never need this but the children/grandchildren might some day". Yes, there is always "some day". Planning for the future. Or, rather storing for the future.
One of George Carlin's many great talks is about stuff. You can probably find it on the web.
Moving means one is forced to reconsider a lot of stuff. Some is crap:
"Hey, it is crap, but it is MY crap!"
Some can be useful to unknown others and donated to charities. Just be careful not to donate crap. One person's crap might be another person's utility. But there are folks that call charities to donate their old furniture that is really crap. But they avoid taking it to the dump themselves. Lazy assholes. As a side note, we do have a good system of recycling in Sweden, though I suspect not all electronic and chemical waste actually does not get dumped on places where they are not desired.
Another motivation for saving stuff might be that it is worth money. Some day in the future. Like that old ashtray, or a snorkel of unusual design. But why save it? Try sell it now or give it to a collector friend.
Then there are those things we associate with persons. Some of which are no more with us. I have some of those things. Some are furniture I love and I consider heirlooms. Not that they are valuable things from the 18th century or so. But they are valuable to me. And very useful. Some smaller things that I connect with past generations are not valuable (I doubt it) and not useful, but I still keep.
Easy-to-rid-oneself-of-stuff are things that we associate with persons we do not care for anymore. It can sometimes even be a catharsis of sorts.
It is amazing how one can find stuff one didn't know one had. Rich people with old castles probably experience that, and maybe we non-rich people in some weird twist of historical "progression" are mimicking that.
Storage. In the U.S.A. it seems storage facilities are used a lot. Maybe people over there have "more stuff!" (to quote Carlin), but I guess it is also caused by the higher spatial (but lesser social) mobility of the society. I myself have used storage for a while. It is only temporary. It is convenient. A necessary evil. Yes, I know "necessary" is personal, subjective and a trifle hoardish.
Moving house is fucking tiresome. It is even more tiresome when one is fatigued to start with. However, it is a forced opportunity to do some housecleaning, mental and otherwise.
I've even gotten rid of a few books. I like books, but I can't keep everyone of them. And I do not want to buy any more bookshelves.