It only prevents it when it's there.

Thr cardboard/newspaper prevents germination of new weeds, and blocks off light from old weeds, generally killing them.

I used this to reclaim a wild patch into a garden bed with cardboard and pine needles as mulch. Took a few months, but it even killed some blackbeery brambles. They came the fuck back of course, but it was enough to get the patch going right.

Dont use colorful or waxed cardboard, and remove all tape. Its annoying, but better than picking it out of the garden later.