I've fought this battle with my DH with some moderate success but perhaps he isn't as attached to his junk as someone else might be. Every time he said he wanted to keep something "just in case", I persistently (I *tried* to be respectful...) got in his face about it - why? is it worth the space it's taking up in our tiny home? You haven't watched this/read that/worn that in years - don't you think it needs to go?
At one point DH had a collection of 40+ button-down shirts. Most in good condition but impossible to keep laundered and put away - they just wouldn't fit anywhere and some of them would go years without any wear because they were at the bottom of whatever pile in the bedroom...dusty. Ick. Anyway, I explained to DH that part of my problem with keeping up on laundry was that I had no place to put things...wedging things into the closet/drawers took so much effort and I really only ever wore the same 2 skirts and 4 tops anyway...so I downsized my own wardrobe in a big way. Then I figured out what the kids really needed and the space it had to fit in and got rid of more stuff. DH was the only one left in the house with unruly stuff. So he got on board.
I still find that I need to do a fair amount of hand-holding while he sorts through stuff as it's just too much for him to decide what to get rid of. This fall I finally insisted we put a playroom downstairs as I needed a place for the kids to be able to go and make a mess without feeling like the main floor of our 950 sq ft was constantly trashed. The room in question was, of course, filled with his junk he'd been promising to sort for years. So I did it. I told him what I was going to do and he didn't object. I mostly knew what he would really need to give an opinion on and set those items aside. The rest I tagged as garbage, donate, or keep. I gave him last check before anything went out of the house but, surprisingly, he wasn't really interested. He did tell me afterward that he *felt* much less cluttered now that the icky job of sorting and getting rid of was done.
Sometimes, if you want the stuff gone, you have to initiate the project and follow it through - as respectfully as possible.
We also no *really* limit what we buy. "Where will that go?" is one criteria we use. "We already have something that does that job." is another. Clothes continue to be a battle for him but I can usually convince him to get rid of one item of clothing for each item of clothing he brings in...