I'm a big stickler when it comes to having the actual case for my disc games. Cartridge games, not so much. If I'm in a Gamestop store & see a game in the used section, with & without a case, I will buy the one with the case every time. The way I see it, since there is no discount for buying a game without the case, I believe when buying the one with the case, you are getting more for your money.
I also have to be honest, I have resorted on occasion to raiding Gamestop's dumpster & have found some interesting items, Game cases mostly. I've even sold them on Ebay for a small profit. The problem is, I started finding other stuff, which I thought I would be able to sell, but haven't. One of these days, I'm going to have to go through the spare bedroom & toss out all that stuff that I thought would sell. ...Anyways, I'm getting off topic.
When it comes to my PS1 games & PS2 games, I keep the games stored in a CD book. The PS1 games are kept separate from my PS2's.
Most of my PS2 titles have the original cases with the game. I use the cases as a display. I generally will try to get my favorite & rarer titles to stand out. I keep all my PS2 games together, alphabetized, & don't split them up based on region (US, Japan, & Europe). Since I have amassed a massive PS2 game collection across all three regions, it almost becomes a chore, when I insert newly received games into my CD books (since they are alphabetical). That collection is spread across 4 massive CD books.
My physical PS4 games on the other hand aren't stored in a CD book. I keep them stored in the original case. Out of my current 385 PS4 game collection, I only have one game that doesn't have the original case & that it Injustice 2: Legendary Edition. I bought the game off of Gamestop.com (I'll never do that again) & they sent me the game without the original case. Those cases are kept in these bags that are designed to hold Blu-Ray cases. I currently have 8 of them filled up. Each bag holds about 46 cases. Once my stack of loose PS4 cases with games gets too big, it'll be time to fill up another bag.