I use office supply store white cardstock for:
- liners for dark colored cards
- test printing before I print journaling on my best cardstocks or vellums
- testing cuts on the Cricut (usually use a blade depth of 4)
- creating masks using the Cricut or punches
- testing paper punch images for size
- white matting for photos or card designs - Often my white mats are in between the photo and the next color of matting so it never looks flimsy.