I've been considering doing a Youtube video about how to maximise storage space for your collection, but realistically I'll probably never get around to it, so I'll just infodump some of the main points here.
If you're using regular bookcases for storage, the first thing you learn is that you can fit more items in by stacking them vertically rather than having one horizontal row.
If they're as tightly packed as the ones shown above, the main thing to remember is to leave enough room at the top of at least one stack for you to fit your hand in. It's easy to get overenthusiastic, fill them all to the top, and then find you can't get them back out again.
If you have longer shelves, and they're deep enough, then a couple of other configurations become possible.
This wrap-around maximises the amount of items you can display while still being able to see the spines for all of them. Depending on the length of the shelves, access to some of the back stacks may be a bit awkward.
This is more of a sliding block puzzle configuration. You can fit more items in than the wrap-around, but you can only see one rear stack at a time. However, you can easily access any of the rear stacks by sliding the front ones left or right. The important point for this one is having a smooth laminated surface on the shelves, otherwise the bottom item on the stack will get scraped.
If you collected TV series on DVD in the 00s, you probably have a lot of single volumes rather than box sets. For me, one of the big space-savers was when I bought a bunch of six-way DVD cases and moved all the individual volumes into them. The six-way case is the highest capacity I've found that retains the spine width of a standard single case, which allowed me to reuse the cover from the first volume of each series. If you look at the first photo I posted, you'll notice that some of the DVD spines have a round, green sticker. That's a reminder to myself that it contains the complete series instead of just the first volume. I then file away all the other covers.
The nuclear option for maximising disc storage would be something like these:
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In that case you lose the covers altogether and just file away the discs in folders. I've considered this for some items, but haven't quite reached that point of desperation...yet.