It depends on the scanner and its software.
Unless you fiddle around and tell it to do something differently, my Canon scanner sends scans to a folder called "MP Navigator EX" inside the Pictures folder. Within the "MP Navigator EX" folder, scans are in their own folders according to date.
Your scanner may organize things differently, but, if you look closely, there is likely a way to save scans where you want them to be. I have to do it every time, or the scan goes to that odd default location.