It’s fairly trivial to clean up the game in a way so the components don’t spill around. First, ditch any vac-formed insert or at least don’t rely on it to ‘hold’ anything. Then basically just pick whichever edge will become the ‘bottom’ on the shelf and stack all the components against it. Start with the heavier things like decks of cards on bottom and lighter bags of tokens on top. A full shelf allows games to hold their neighbors closed. When taking a game from the shelf you can rotate a neighbor on its Y-axis fill the gap and press against the other boxes (if needed). For particularly troublesome games, silicone x-bands are a good option. (edit) Perhaps I should clarify that we store all components in small ziplocs or food storage containers.

My main grip with horizontal storage are the hassle getting games in and out of the stack. There’s also the issue of dishing and split corners from the weight of the boxes on top pressing on the boxes below. And, if they’re stacked ziggurat style, then it’s not efficiently using all the storage space available.

Personally I’m a big fan of vertical storage. It’s so easy to take whatever game you want. In horizontal storage the game placed in the bottom is going to be harder to remove. I also don’t like having a game supporting all other games on top, feels like an unnecessary straining of the box.

I prefer the aesthetic of vertical. There’s just something about it that makes it look like a “proper” collection to me. Of course one downside is that it’ll definitely mess up the components if they aren’t in baggies or some type of organizer.

Vertical with the GeekOn Box Bands.

I use the GameGenic Token Silos, Arcane Tinmen sleeve and tuck boxes, and soon the GameGenic Token Holders to keep things from getting messy inside

Mostly horizontal, but for games with lots of little pieces (I’m looking at you Wingspan) we put the pieces into little ziplock bags so they don’t get jumbled.