JÖCKÖ HÖMÖ: HDD prices are still stagnant here and having all your data on a large disk is a problem if it breaks and not many people will double their HDD cost to mirror data.
Maybe there is no need to mirror the data, as long as GOG servers are still online. Your games on the GOG servers are your secondary backup.
Only when it seems GOG might be going to close their servers, I'd start fretting over having backups of a backup of my GOG game installers.
Also in my experience HDDs generally start giving some early warning signs about becoming broken, at which point of course you copy all (or as much as you can) of its data to some other HDD. Only once I recall zapping a hard drive in an instant, I was careless with static electricity when handling a hard drive. I don't throw HDDs around and I don't have a dog that would eat my homework and HDDs.
SirTawmis: Or even if there was a way to "Check" mark specific games. Say you have 100 games, but you just want to download the "Sierra Games" - so that's like 40 games. You check mark those 40 - and it just downloads all 40 games when you click "Download All" - maybe a check mark "Include Extras? (Y/N)" type thing.
All of this is pipe dreams, naturally. GoG probably doesn't want their servers throttled like that, hitting a lot of downloads all at one time from a single person.
Well. at least some of us, including me, are at least occasionally downloading all our GOG games (and updates to them) to local backups, either manually or using tools like gogrepo. I haven't done that for several months now, maybe it would be time to refresh my local GOG installer library...
Anyway, if GOG wanted to ease the pain on their download servers, they could add some kind of optional peer-to-peer protocol, so people would not download data only from GOG servers, but also from each other. E.g. Humble Store has used that for many years already, they provide you optional bittorrent links to downloads (or you can also download directly from their servers). Heck even my phone's car navigation software (MapFactor) has the ability to download gigabytes of offline world maps also from other MapFactor users, using peer-to-peer protocols with the phone (or alternatively just download those maps directly from their servers, if you don't want to use p2p).
Anyway I guess GOG has more important things to think about than serving the ability to mass-download GOG offline installers, which I presume only a tiny fraction of GOG users ever do.