Depends what you're needing. If you need white in the decal, that's what the white paper is used for. Since ink jet printers can't print white, there's no applied in white ares and the white paper shows through. Sometimes even that doesn't do it if it's too hard to cut exactly around the image. I had a bunch of bumper stickers I needed for a van build and I did them on white paper to get the white lettering. They were nice and rectangular so were easy to cut out. You can see them in my WIP here: near bottom of page.
Most decals want to be printed on clear decal paper so there's no close trimming to do.