Since this forum will be populating soon with people installing Deus Ex Revision, DE Mankind Divided, and then rediscovering DE mods like The Nameless Mod, a few of them might be first-time PC builders.

So, as a newbie and first-time builder, I think this option causes a lot of confusion for them. I'll use my example:

"Should I choose 32GB (4GBx8) or choose 32GB (8GBx4) for MSI X99S SLI Krait Edition ATX?"

While the the four 8GB sticks are advertised as being able to upgrade in the future, it doesn't explain why we have the eight 4GB option which fills more of the motherboard.

I can't find a technological reason why this choice exists, or why companies continue to sell eight sticks in a pack.

I don't know any computer that supports 8 sticks of RAM, aside from servers. So for regular consumers, this is moot.
If you're running a server farm, though, it is quite a logical choice to get multiple identical sticks of RAM. Once one fries, you have an immediate replacement - that's what Google does with her HDDs, at least.

(to start with, link to the board he's talking about) A lot of what you do with things like CPU and memory depends on the board you end up with. The memory is specially true in this regard. You're stuck into a particular thing by the mainboard you select (I'd look for something cheaper than that one that is good quality, it is really a server board like Made in China talks about).

As far as that board is concerned, it supports 4 pairs of memory with a varying number of specs. You always want to buy the highest spec that the board supports that is available. With that particular board it's DDR4 3110. Whether I went 4GBx8 or 8GBx4 depends on what the board specifically supports, and how much they cost. Speaking of which I might go 16GBx2 if it's a good option. Looking at Newegg, 8GBx4 is going to be preferable which is about $300 for this board.

But as Made In China, a lot of it is preference and what someone wants to do with the machine. A lot of that is due to the fact that 8GB sticks didn't exist once upon a time and if you wanted 32GB you needed 8 sticks.

But the general answer to the question at hand is that most of your other options depends on the board you select. Select the board, and the rest of the options just follow. Of course, selection of the board depends on what you want and what you want to do and the budget you're under. Personally, I'd look for a different board to start with, but that's just my mind in building a non-server gaming computer.

My opnion really only (barely) matters if you're building a gaming rig:
32 GB seems a bit overkill to me.

Even if you look at recent AAA releases (twitch3r, MGSV), they only recommend 8. So it seems to me you could save a decent amount of cash for little performance downgrade by getting 16GB instead and still be futureproof for some years.

As for getting 4 sticks or 2. It depends. Afaik sticks only work in pairs, so if one breaks your computer might stop working if you only have 2. Only getting 2 means you have 2 slots open if you eventually want to upgrade though. However, 4x4GB might be cheaper enough than 2x8GB that it's worth it.

I use 4x4GB.

I agree the choice barely matters. One thing to bare in mind regard Jaedar's point on upgrading is that when the next generation of DDR comes out, the old generation always seems to get more expensive (presumably because they stop making it).