In applications like inDesign and Photoshop, you get to chose which color model you want to use, RGB or CMYK for instance. But why does this matter?
Both RGB and CMYK can be used to describe several millions of colors, so there's no shortage in the possibilities of either of them. And I do know that the origins of e.g. the CMYK color model lies within the color composition technique used in printing; and of course black is described either by 100% Key in CMYK or 000000 in RGB, but this doesn't seem to matter anymore. Even if I use RGB Colors in inDesign and print the document, I will still get the right colors on the printout (due to internal color handling in either inDesign or the printer, I assume).
So given all of that, why does it still matter whether I use RGB, CMYK or something entirely different in inDesign, Photoshop and the likes?