Yes but that's a practical consideration more than anything. Besides, you can always split your system drive into two partitions and have the second partition for data. That way you can safely reformat the system partition and reinstall the OS without having to worry about losing any of your data. Most people's system drives are way too big just to be used for the OS and installed programs. My system partition, for example, is 469GB according to Windows. And even though I have a ton of programs installed on there, I'm only using 100GB of it. If I reserved the entire drive simply exclusively for the OS and installed programs, I'd be wasting hundreds of GB of storage. Hence the popularity of partitions, which are a piece of cake to set up.