I only have one sealed PC game - and it's a re-release of NHL '98, nothing valuable. When I'm ready to really sit down and play it, I'll tear the shrinkwrap off and consider that part of the experience of enjoying the game. Honestly though, I expect there's nothing in there but a thin black and white manual and a CD case. But if I'm lucky maybe there's a full color advertising brochure for other games.
I don't have many boxed PC games because ~15 years ago I threw a lot of my old boxes away. I kind of regret that, but they do take a lot of space if you get too many. I'm just glad I kept the Ultima boxes because damn, those things are valuable nowadays. Enough that I'd consider selling them if I wasn't so sentimental about them.
Recently I ended up with a boxed NES game (the price was good). I was conflicted about that because I really don't like old cardboard Nintendo boxes, I think they just look messy and were intended to go in the trash. But I can't throw it away now, because it's too old to treat like trash anymore. I've decided it's cool to have one NES box to look at, but I don't want to collect them.
Sega is totally different because they had nice boxes that were meant to be kept. I've been surprised how many loose SMS and Genesis games are out there. It just seemed natural to me to keep those boxes, but obviously a lot of people didn't.
When I moved from California, I used thick (6mil) plastic sheeting with a heat sealer to seal several of my Genesis games. I did that to protect against humidity during the long shipping process.
One of those games is Michael Jackson Moonwalker, which is a game I really don't care about and might sell off at some point. I'm thinking about leaving it sealed in it's little biodome, just so I can tell people that even though I live in Florida the game still thinks it lives in California and has never been exposed to the humidity.