A lot of software, including Windows, writes temporary housekeeping or index files to your drives. A prime example is the thumbnail file Windows creates for images when you display them as such. This file can actually grow quite large. With today's vast hard drives, the file system flotsam on your PC hardly matters, but your USB flash drive often doesn't have space to waste on such temporary files. USBDriveFresher automatically deletes these files so you can maintain the maximum amount of free space on your thumb drive.
There's not a lot to configuring USBDriveFresher. Install it, run it, and if you need to, add a file type to the already well-populated list of those that should be deleted. You may run the program manually, or have it start up with Windows. Either way, once run, the program sits in the system tray until you stop it. You have the option to have it do its job silently, or inform you before it deletes files.
Although USBDriveFresher is a nice concept, I'm not sure that the problem it tackles is serious enough to warrant a full time system tray applet using 7MB of memory, even though it uses an admittedly small number of CPU cycles. Hence, if you don't know how to delete hidden files manually, or aren't sure which ones can be safely deleted, download USBDriveFresher. But just run it manually when you think your thumb drive isn't offering its full capacity.