When browsing the assets, there is a "Temporary Uploads" folder. What is it for? Can I disable/hide it?
Each user account gets their own "temporary uploads" folder that by default will be a subfolder under
There are several places there this is used in Craft... one example is if an Asset field has its "Upload Location" set to something dynamic based on the value of another field. When saving a new element, Craft won't know the value of that upload location until after the element is actually saved, so it keeps the uploaded file for the Asset field in the "temporary uploads" folder, then moves it out of there after the element has been successfully saved.
Can I disable/hide it?
You can't disable it natively, but you'd probably be able to use some CSS to hide it if you really wanted: https://github.com/doublesecretagency/craft-cpcss