Quoted from jar155:

What makes our hobbies or passions any more important than those of our significant others? While you might not see a point in extra couch cushions or scrapbooking supplies, it doesn't mean that your spouse, girlfriend, or boyfriend doesn't love them as much as you love your pinball machines. The "man cave" mentality is dangerous. To create a space that isn't shared with your significant other in a home where you live together...that's really odd.
Put your significant others, kids, and friends (and any living being, really) ahead of any possessions and life will be better. I promise that. If my wife came to me and said, "you know, you have more than 20 of these pinball and arcade machines. Don't you think we could do with 5?" we could have a discussion on that. If it's because she doesn't have space for her things, then I've been in the wrong to fill my house with this stuff without proper regard for her wants and needs. If it's because she can't understand why I want so many, we can talk about it and I can explain. Thing is, I know it won't come to that because as she allows me to have my space and passions, I do the same for her. If one should encroach on the other, you work it out. There's no "I AM PUTTING MY FOOT DOWN!" That's caring more for stuff than people.
Kids hoard their toys and keep them from their siblings. Let's be a bit more mature than that.
And really...do any of use NEED any of these things? They're great, but a great companion in life is far more important and enjoyable.