For the setup files, I mean.

I have one but I want to clear some gbs off my pc.

Yes. I have an internal HDD (4tb), this is my working drive alongside 2 SSD's. I then have four separate 4tb HDD's which at quarterly timepoints I copy the working drive onto. These are stored 2 * locally, 2 * not locally. I keep a set of spreadsheets which detail the various systems, what I have, what format, where brought etc. Very simple setup, perhaps just over £400 in total over a year to get the HDD's, and it runs overnight so no time lost. Simple and effective, totally offline, download via web browser so no additional software, and no reliance on a web site or client software. Its mine, and its damn well staying with me :o)

I Go Grepo my GOG games to an external drive.

I keep my stuff in an external HD that I only connect to the PC for backup purposes.

Yeah, where the downloader puts them all pretty much. When I decide there's a need to move the nearly 300 installers, I'm sure I can do it then.

No. I'm pretty sure GOG has plenty of backups themselves. And I don't see them closing shop in the near-future.

Yes, a 2TB NAS.

A USB hard drive. Easy enough. Not the fastest thing around but the backups can occur in the background so speed isn't really an issue.

I use lgogdownloader (third-party downloader for Linux) to download everything except non-english languages and mac binaries. This currently uses 383G with my set of 253 titles with some earlier versions remaining.

nope no backup folder here i have to admit. Don't expect gog to go out of business anytime soon so don't really feel the need and it would be requiring a lot of HDD space as i own some of the newer games as well besides the goodies.
Got a really fast internet connection though so i kinda can get all games "on demand" anyway and for the very very unlikely case in the far future that gog closes someday i expect them to notify us in time to backup anyway

Not picking on you particularly here, but there seems to be this vein of thinking that GOG will always be there. I find it interesting. My one big beef with DRM for instance, that DRM which requires internet, is that at some point it will stop working. Hence relying on GOG being here is pretty much the same crutch.

Two to be precise; one on the internal HDD and another one on an external HDD that is used only for keeping backups. When not taking backups, it is stored inside a titanium safe that in turn it is stored in another, bigger tungsten safe, guarded by military dogs and a laser alarm system. Safety first!

I have a backups folder yes. Once I decide its so much and I need my space back, I have my blank DVDs to burn into. Never am I going to buy a PC or a laptop without an optical drive, so it works for me.

Three. My internal HD's folder, and my two extrernal backups. My internal HD is getting saturated, though, so, I more and more remove stuff from it and keep it on the backups only. That's kind of annoying when it comes to update management, though.

My thoughts exactly. The ones that rely on the cloud for their "backups" are going to be the first ones to cry foul and blame everyone else when the day comes that the cloud fails them.

And it WILL come, for every service. No company is forever.

As for me, I keep a base copy of games burned on a CD or DVD (with nice printed Amaray inlays). I keep updates on an external 2TB hard disk.