I'm probably middle-of-the-road on this issue. I have a lot less clutter than any real-life friends, that's for sure! Our house is not bare by any means, but it is small and livable. We don't trip over stuff, like some neighbors in similar homes.
My DH has one under-the-bed size/type of box with all his mementos, including trophies and such. It lives on the shelf on his side of the closet. He also has one scrapbook his mom made for him when he went to college. Normal size binder-style photo album with those magnetic pages (bad for archiving, but not really a big deal to him). He does have more personal, sentimental, random items than I do. Stretched Pepsi bottle, some bobblehead thing, poster-size collage from his track star days, a heavy Darwin sculpture, and random 80s and 90s items of clutter. They are all contained to one room -- our family office.
I had one 12x12 box of mementos that were not scrapbook-able that also lived on DH's side of the closet on the shelf until I photographed the items and ditched them. I do have several scrapbooks that I have made over the years, with the most interesting pictures and mementos (either photographed, or scanned and sized and printed, or flatish ones adhered right in the book) from my life journey. Most of my personal belongings from childhood, though, were given away or thrown out by my step-mother when I left home at age 17. I was mad and sad at the time, but got over it rather quickly. My step-brother let my best friend go into my room a few times to grab some of my belongings before it was all tossed. Thank goodness she is the practical type and grabbed my clothes and shoes and such -- only a few mementos. LOL (My dad and I have settled our differences and are very close now that he got serious help, but I have never seen my step-mother - the woman who raised me from age 8-17 - nor my step-brother since.)
All the scrapbooks and photo albums are in a bookcase in our living room. They go into the laundry basket along with our small fireproof box and laptops and external hard drives in the event of an evacuation (which we'd had twice).
I let DD, age 10, keep what she wants, but we are limited in volume due to our small house and general lifestyle/home decor (not minimalist in a strict sense, but clean, clear surfaces with a balance of empty space with functional items and "pretty" items). She has been participating in the donation process and cleaning process since she was a year old. Yep, I start 'em young! LOL She currently has two file boxes of items she doesn't want in her bedroom, but doesn't wish to donate or recycle at this time. They are opaque plastic boxes with flip-back lids that reside in my side of the closet. We have a double-check system. LOL She can remove items from her bedroom or other personal spaces at any time. She puts them in my closet: one pile for donation; one pile for the aforementioned boxes. I go through the items and adjust according to my attachments. Financial or sentimental, I don't sell anything, but I do find specific new owners of the pricier items and some sentimental items. I do keep some sentimental items that she "donated", but they don't count towards her allocated space. I have an old Trofast storage bin (medium size) from a system we donated years ago where I keep those items.
I also have baby clothes and fabric items up through age 5 for a quilt I have yet to make. I took quilting classes just for this project!!! LOL I know I want to make one large quilt (cuddle-size for her) and one small decorative quilt (art-size for the wall for me). I just haven't found the designs I love yet. Well, technically, I have a picture of the art-size one in my head already, but I want to use the leftover scraps from the cuddle-size one and I do NOT have a specific design idea for that one. One specific baby dress is the focal point of the small quilt that will be handstitched onto a simple scrappy-style background.
And, I am a scrapbooker and LOVE it! So, I do have a lot of her childhood mementos for her books. A few years ago, I gathered everything from preschool and scanned everything I still liked; let DD look everything over; then recycled it all. I HAD 90% of the items in a photobook program when I realized I was missing a good-size chunk. It took me awhile to hunt all of it down (it was filed exactly as it should have been and I have no idea why I didn't check there first! LOL) and when I got it all scanned in and went to add it to the existing online folder, everything was gone. Blah. The raw material is still on my computer, but I haven't gotten up the interest to re-do all the creative work.
I teach art in my DD's school (for five years now). I go to workshops to learn the lessons hands-on and then I teach them in the classroom (8-10 lessons each year times 2). It is a formal art program and I have almost as much art as DD does! LOL We also have family art night at her school twice a year, so DH has some art, too. (He has a hidden talent!!!!) Last year or the year before, I scanned or photographed every piece of art. DD and I used the best pieces to decorate the big blank wall in our kitchen and we change it up every so often from a small selection. We sent some to grandparents (and had been doing that prior to her school days) and we used some as wrapping paper and cards for birthday gifts. DD decorated her bedroom walls with a few pieces (from the "best" category and they get rotated). The majority got recycled.
As I create my life journey scrapbooks, I make a big huge mess with "stuff" and thoroughly enjoy the entire process (emotionally and creatively). A lot of the memories are challenging, shall we say, and it has been the most productive and cathartic form of therapy for me. I adore my finished scrapbooks! Many friends and family love looking through them, too. When I am finished with each volume (I don't do them chronologically, but rather by subject or period of my life), so much "stuff" is sent to friends and family (if they want it) and recycled (and "released"). A scrapbook is a creative expression for me and takes up a lot less room than all the mementos and photographs. DD loves looking through them all. Except for a few small mini albums and DD's baby book, I have a general rule of thumb to cut down on the volume of stuff. If the photos are digital, then the final product needs to be completed digitally (online photobook). (I scan and recycle the non-pictures.) If the photographs are in my hands (pre-digital age), then I create physical scrapbooks with all the physical photos and mementos -- paring down along the way.
All the crafting supplies (photos and mementos included) are contained to the family office, as well as DH's odd assortment of keepsakes. In effect, the only cluttered room in our house is the family office. Most people don't consider it cluttered at all. I consider it cluttered because it is the hardest room to clean and, consequently, is the last to get done.