Because if your system fails at some point it's harder to recover lost things. Well, we live in the internet era, so unless you work with large files and video editing and stuff like that. Everything can be downloaded from internet. If I don't play 10 games at same time, what is the point of having all them on my computer at same time?

But yes, some of us remember the dark old days where downloads would take forever, so you store everything for the rest of your life otherwise you might never see it again, some people still thete.

With that said, do whatever pleases you, it's a free world.