It was suppose to help the user
Temp files act as cache, which allow faster access to opening files ie They are on your computer not the Internet
Logs help diagnose issues that may happen and can be used as a history reference
Registry entries allow reference as well, including back up of searched areas etc etc (this area is big)
And hidden files allow others to diagnose symptoms that the user cannot normally remove
It's all about backup; quicker response and diagnosis
But all these things were improved over the years.
Backup programs are now generally accepted as external
Quicker Response is now available through faster computers
Diagnosis can be made immediately without build up of history
There was another area too.
Poor optimization of written software
MS trying to better improve their developments in Windows, from users activities
But something even more stranger happened since the Internet and Windows users first started becoming a home and basically private area.
Privacy itself was destroyed, and then basically re-written and re-defined
It is now acceptable that private individuals provide all their personal information online. Including Age; Personal Interests; even Photos of themselves, and generally everything about themselves, that was once classed as "private", and certainly never allowed to go public.
This happened through the digital technology, cameras, and the Internet and generally to help in safety of our children or even communities in sharing and legalizing and overseeing of activities (basically the Big Brother approach)
At that initial stage (that all older people are fully aware of - sorry to patronize) The "children" basically grew up, conditioned to allowing "privacy" to be a thing that everyone can see. BUT many older individuals (and some younger with old fashioned ways, still in bred) know that this is not privacy. This is the accidental (and totally originally non-intentional) mistake, that we taught our children to speak openly (about themselves) and allow all their movements to be fully viewed to everyone, not just to the parents
Not to worry, many older and more aware people thought. As safety in the community and sharing knowledge was still generally a benefit in many areas. But, just then it happened ! Something no one ever realized until it was too late.
We had forgotten to teach our children what privacy meant, and now they were adults, and the original adults were quickly dieing off.
Of the few originals left (ie me, and not many others left in the world) try to hold onto what "privacy" is still around (next to zero) And continue to avoid things like Messenger and hold the true meaning of what "privacy" once was, ie private.
Therefore, your questions are generally not understood by most any longer, and even questioned as to why you would even want to remove this publicly accepted area. You are not alone in your confusion, but possibly now realize Windows and the Internet together with Privacy does not exist.