Whenever we are shown Sevens’ quarters, there is a bank of at least three Borg alcoves against the wall.
Why would Seven need three alcoves?
I’m not sure it’s ever been answered or addressed. Perhaps it’s like why I have two spare bedrooms. One never knows?
Alternately, hey, Borg threesomes?
I figure they are built in multiples and it was easier to grab a three-pack and hook that up to power and other supplies than to figure out how to pull them apart to get just one.
I never got so far as to look beyond chest level.
Yes.
It came in threes.
So the show could have an arc for those 3 kids they picked up. What would we do without that? I have always wanted to know what happened to the little Borg baby?
IIRC, the alcoves were salvaged from a derelict Borg ship. I would assume they were just built that way and maybe wouldn’t work if you tried separating them.
Well I suppose that’s as good an explanation as any. Thanks for your input, all.
As I recall it, when the board first came aboard voyager, there was more than one. The crew had to get rid of most to avoid an insurrection, and only Seven survived. But I could easily be wrong, not having seen the series (ha!) In many moons.
I imagine there was just one but it assimilated a nearby coffee maker and toaster. (And you thought Neelix was mad about losing Kes.)
Seven comes aboard in Scorpion Part II (first episode of season four.) Her Borg cube is destroyed by Species 8472 and she transports with Janeway to the Voyager’s cargo bay with several drones and several alcoves. Screenshot. The other drones are eventually killed but Seven gets de-borgified. The three alcoves on the wall were kept because they presumably come as a single unit.
Pretty sure you can still buy those plastic plasma discs at Spencer’s Gifts, too.
When they tore down Busch Stadium in St. Louis a couple of decades ago, I knew a guy who picked a group (either three or four) of seats. They were a single unit. Simple as that.
I believe you are giving Voyager more thought than the people making it ever did.
Redundancy in case one fails.
This would be my fanwank.
As a matter of fact, I vaguely remember Seven scolding Harry because Voyager didn’t have TRIPLE redundancy.
The Borg really only understand redundancy through extreme application of distributed systems. But there are other ways to achieve suitable redundancy. Just because Seven doesn’t like Starfleet engineering doesn’t mean it’s necessarily inferior. 
Well, Voyager did have triple redundancy, so it could keep going even if some systems failed. And then, well, some systems failed, and it keeps going. That’s how it’s supposed to work.
3-ways?
As others said I always assumed they just took a chunk of a Borg ship and that was how it was.