I've only saved a few letters, just a couple that have made me laugh and a couple that were really sweet. I got one from Deirdre about how she worked and worked at growing hybrid flowers and she FINALLY got one and promptly sent it to me, I thought it was nice so I kept it. Other than that I just discard them because they're mostly repeats anyway.
I've saved a bunch when I first began to play but since then cut back to little to none. It really has to tug on my heart strings for me in order to keep.
I always forget or am too lazy to save letters... I have done so for a couple, but I've also accidentally tossed away a couple (bye, Graham... you wrote the sweetest goodbye letter).
I saved all the event furniture in new letters. For Easter, Halloween and Snow items you get the set the first year. After that it turns into repeats and it's hard to complete the set again. I buy new letters and write what is inside. It makes it easy to find the items.
Other items I saved are the extra Gracie clothing, rare writing paper that came in the mail and HHA stuff. In the early years I did save a slot full of perfect fruit just in case something happened to the trees. The rare writing paper got removed from the catalog so those are collectors items.
I saved Muffy letter when she moved out. She was the only villager that I let go.
I only save the goodbye letters from villagers that have moved out of my town. That way it's like a rolling record of which villagers I've had over the years.
I like to keep some of them. I am currently recovering from oral surgery and my teeth are wired shut and I can only drink liquids until I'm better and by coincidence Zucker sent me a letter telling me he has a canker sore (lol) and he can't chew or talk (I am super frustrated about not being able to talk especially rn) and he's only have like ice cream until he's better. AND IT MADE ME FEEL SO MUCH BETTER for some reason. hahaha Like I know it's just a coincidence but I was just like, omg. i feel u. So I saved that one. I think I've saved a couple other funny ones.
I only save the last letter that they send after moving and the ones after giving them gifts for their birthday.
Sometimes, I write their Toy day wishes and save them.
I did early on, when I really needed extra storage. I've kind of cut back on what I save now, with the museum exhibit rooms, a full house, and secret storage.
I know I used it a lot back when I played ACGC, especially for saving seasonal items, so I could switch my house around.
i've always saved parent letters and moving letters as a kid in my first ac game. since i'm sorta playing out of nostalgia i guess it feels wrong not to continue it out of habit.