Hi there guys!

I had to reset my PC and reinstall Windows from scratch because I had a few annoying issues like - among the other things - some games and programs not starting because of vcredist related issues (mostly 64bit games/programs).. I suspect most of the issues were related to those MS C++ redistributable packages that every game wants to install. I understand those libraries are needed etc but I didn't understand why I have to install 2 or 3 version of the same redist package!
I wanted to verify if I really needed different version of vc redsit 2012, for example, so I try it with a clean Windows installation.

So, I reinstalled Windows. I previously made backups of all GOG and Steam games so yesterday I started to restore them. I started from Steam: Steam uses a vdf script file to check if "dependecies" are satisfied; once you install Directx June 2010 the vdf script detects the installation thanks to a registry entry and next time it will skip it for all games (but it downloads it anyway, but that's another story). Same happens for vcredist packages.
But the problem about vcredist is that there are many different version of the same year, so for example vcredist 2005 6.66.66 is indeed different from vcredist 6.66.67. If a game requires a version you don't have Steams asks for Administrative permission to install it. I denied permission and - as I thought - the games work fine, so now I have only one version of vcredist for each one.. Naturally every time you start the game it will ask you for Admin permission to try to install, but I renamed the vdf files adding a _ at the start of filename and it's done.
At the moment I'm writing I already restored half of my games and skipped a bunch of vcredist installation and all games work. Maybe I'll find a game absolutely requiring a specifc version but until now that didn't happen.

Then I started to restore GOG games. I installed all my games via Galaxy so I restored them importing the folders on Galaxy again.. Here happened something weird..
First thing is more a glitch: Galaxy detects the imported games version as - example - v.2.02-gog but in the Settings tab warns you about that version being old and not available, thus suggesting you to install the.. v2.02-gog :D That's a glitch, as said, nothing really important...
But what I don't understand is how Galaxy is able to install redist packages without asking for Admin permissions! All it does is downloading dependencies and installing it directly: all of sudden you see the vcredist window installation but you gave no permission to install it. Those packages install system files into System32 folder (or SysWOW64 one) so Admin permission should be absoutely required!
I had issues with Crysis 64bit version before reinstalling, so it was the first game I restored and verify. Once I saw the vcredist installation windows I immediately clicked Cancel for both packages (x86 and x64), so it did not install them. Then I started the game and it worked, using the vc libraries version I already installed for other games. Untill a few days ago (untill reinstalling Windows, I mean) I had to manually start the game from Bin32 folder (making Galaxy totally useless - I posted the issue here: https://www.gog.com/forum/crysis_series/crysis_64_bit_does_not_start ).

What I like is that Galaxy seems to have a better management of those required dependencies and libraries, placing them in a separate folder that future games you will install could access; required packages are signed into a goggame-galaxyFileList ini file: I'm still not able to tell if those files are really downloaded only once (per version, indeed) but the system they created make me think it (unlike Steam that really downloads the same Directx June 2010 billions of times, a non-sense and something fool, if you ask me).

I don't use Galaxy myself so can't answer that part.
What C++ issues were you facing? I have about 10 versions installed and only if a game doesn't run would install any further ones. Its always the same though with any dependency, DirectX and all those. Like as not its this need to have everything installed all the time. Personally I keep maybe one or two games installed at any one time (everything installed outside Windows folders!), and remove anything I don't use immediately. You only need to keep the installers (90% of the games here are tiny and only need a minute or two to install) of each one.

As for why they were needed, you'd need to ask the developer on each game for that information, you can only program with what is available at the time, and its not always within your control to enforce backwards compatibility.

as I said, issues were like games and programs not starting anymore for an error related to vcredist packages (as linked above).
also Galaxy directly installs dependencies without asking for Administrative elevated user permissions; I'm able to skip dependencies installations on Steam and check if game is working with ones I already have, but not on Galaxy.. it goes straight on without asking anything