It is really a pain in the ass. Imagine you install 5 games consecutively, and all of them update DirectX after installation, while you already have the latest version. You never know if they leave the latest version intact, overwrite, or downgrade it. And some stupid games even install VC++ runtime when your computer already has it installed, making your Control Panel program list full of VC++ Redist. And of course, the corresponding VC++ runtime is NOT removed when you uninstall the software. Currently, I have to track and write down which software installs which version of VC++ runtime, so I can remove it when I uninstall the software.
Some pirate groups repack the game, change the installation wizard, add optional DirectX and VC++ installation options. In case your forget to check them, you can always install them later by browsing the setup disc/folder. If you ask me, I prefer the repack version over the original disc in such cases. Pirates are smarter than the game developers, indeed.
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TheVillain PCSX2 requires the latest (well, almost latest) DirectX and VC++ runtimes. If you want to run PCSX2 on multiple PCs, prepare these runtimes installers as well because they may not have been installed. PCSX2 don't automatically install these things into your computer. One reason for me to like PCSX2.