The minimum requirements for windows OS are far bigger than they realistically need to be, because at some point in the past someone took Microsoft at their word. Installed it on a drive that was near the absolute minimum and then a few years later didn't have enough space left to install an update.

So nowadays MS likes to err on the side of caution. And figure what people actually need to run the OS, plus typical minimal applications disk requirements, plus swap file, plus space for updates and logs plus a healthy margin just in case.

You can try to get away with much less than what Ms says is minimum requirements. You probably shouldn't.

With hard drive space for consumer computer being nearly dirt cheap and for servers being mostly virtual and adjustable, this really shouldn't be an issue in most cases anyway.