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. And why that stuff needs so much space on my HDD (I have only 200 GB) is beyond me. I understood what's in the RAM should enhance the performance and make it easier with the programs that are opened by the users.

Well for one thing, Windows will make a page file equal to the amount of RAM in your system (plus 300 MB) and that subtracts from available HDD space. It will also create a hibernation/sleep file equal to your system RAM, where it stores whatever is in your RAM on the HDD when you put your PC to sleep.
Lowering your page file size and eliminating the hibernation file will regain a lot of HDD space, if it's a problem, but if you remove your hibernation file (actually called "hybrid sleep"), you won't be able to put your PC into sleep/hibernation mode.

So if you have 6 GB of system RAM, that's almost 12.5 GB of HDD space right there, and it could be more if you have an OEM with a preinstall that set your page file size higher.