Capture One 4 is RAW workflow software. The software provides a step-by-step workflow through the image optimization process, allowing you to work with large volumes of images.
The Capture One application creates a cache folder under its PhaseONE software folder under Program Files, but seems to store all its C1S files in the My Documents folder. You can change this using the program Preferences.
After opening several folders of RAW photos, you can end up with 64K+ C1S files which may take a long time to open. There is a setting that is supposed to delete the cache when the application closes (one user reports this did not work for them).